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The geology and genesis of the Central Zone alkalic copper-gold porphyry deposit, Galore Creek district,… Micko, Janina 2010

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THE GEOLOGY AND GENESIS OF THE CENTRAL ZONE ALKALIC COPPER-GOLD PORPHYRY DEPOSIT, GALORE CREEK DISTRICT, NORTHWESTERN BRITISH COLUMBIA, CANADA by  Janina Micko  MSci, The University of Birmingham, 2005  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in  The Faculty of Graduate Studies  (Geological Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  December, 2010  © Janina Micko, 2010  ABSTRACT Located in the Late Triassic Galore Creek alkalic Cu-Au porphyry district in northwestern British Columbia, the Central Zone deposit represents the end-member of the silica-undersaturated class of alkalic porphyry systems. The deposit is hosted by volcanosedimentary rocks of the Middle to Upper Triassic Stuhini Group that were intruded by a syenite-monzonite complex and hydrothermal breccias. Post-mineral tilt (45 to 60° W-SW) provides an opportunity to examine a vertically extensive depth range of the system, and the impact of host rocks and a redox control on the precipitation of sulfide and silicate alteration minerals. Early mineralization associated with potassic alteration is dominated by gold-bearing chalcopyrite + bornite (Cu:Au ~ 2:1). A second gold-poor mineralization event is associated with calc-potassic alteration and dramatically changes the Cu:Au ratio (5:1) in the core of the Central Zone. In general, greatest Cu-Au concentrations overlap lithological contacts characterized by contrasting ferromagnesian mineral content, thus forming redox gradients. Sulfur isotopic compositions emphasize the importance of fO2 conditions in ore deposition. Sulfides in highly mineralized centers are characterized by moderately negative δ34Ssulfide values (-10.66‰ to -7.84‰), whereas sulfides deposited distally show highly negative δ34Ssulfide values (-17.13‰ to -4.03‰). These data suggest that the interaction of sulfate-rich (SO42-(aq)) fluids with varying amounts of Fe2+-bearing minerals in host rocks increased H2S/SO42- leading to formation of reduced S, and precipitation of sulfide minerals. Trace elements such as V and As in host rocks and Eu2+ in hydrothermal garnet reflect the same redox influence. Vanadium and As are soluble under highly oxidizing conditions. The shift in oxidation state facilitates their incorporation in alteration minerals. Thus, highest V (>700ppm) and As (>40ppm) concentrations form halos distally to the redox gradients and ore ii  bodies. Hydrothermal garnets near lithologic contacts contain excess Eu2+. In contrast to V and As, Eu2+ is soluble in reduced fO2 conditions and precipitates close to the redox gradient. This study demonstrates that redox is the dominant control on ore deposition in the Central Zone. Recognizing redox changes may provide a valuable guide for future exploration in the Galore Creek district and perhaps other alkalic Cu-Au porphyry systems worldwide.  iii  PREFACE This thesis consists of four manuscripts that have been prepared for future publication in peer-reviewed international journals: Chapter 2 represent the first manuscript of which I am the lead author. Richard Tosdal, Claire Chamberlain, and Kirstie Simpson are the co-authors and initiators of the overall research project. As the lead author, I conducted field work, collected samples, and carried out all analytical studies. The latter was supported by Mati Raudsepp. In addition, I designed the bulk of the text, figures, and tables. All three co-authors provided technical advice and suggestions both in the field and during manuscript preparation. Richard Tosdal and Thomas Bissig, another member of the research group, contributed to revisions of the manuscript. The reference for the manuscript will be as follows:  Micko, J., Tosdal, R.M., Chamberlain, C.M., and Simpson, K.A., Lithological description and interpretation of the host-rocks of the Central Zone deposit, Galore Creek alkalic coppergold porphyry district, northwestern British Columbia, Canada.  Chapter 3 has been submitted for a peer-review international journal. I am the lead author, whereas Richard Tosdal, Thomas Bissig, Claire Chamberlain, and Kirstie Simpson are the co-authors. As the lead author, I conducted field work, collected samples, and carried out the dominant portion of analytical studies. The latter was supported by Mati Raudsepp. Richard Tosdal conducted a geochronological analysis (SHRIMP-RG) of titanite samples, interpreted the acquired data, and designed the associated text, figure, and table. I produced the remainder and bulk of the text, figures, and tables. All three co-authors provided technical advice and suggestions both in the field and during manuscript preparation. Richard Tosdal and Thomas  iv  Bissig contributed to revisions of the manuscript. The reference for the manuscript will be as follows:  Micko, J., Tosdal, R.M., Bissig, T., Chamberlain, C.M., and Simpson, K.A., (in review), Hydrothermal alteration and mineralization of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada.  Chapter 4 is intended for submission to a peer-reviewed international journal. I am the lead author, whereas Scott Halley, Richard Tosdal, and Thomas Bissig are the co-authors. As the first author I aided in design of the overall study and collected the required samples. The analysis of samples was carried out by two commercial labs, ALS Chemex, Canada, and the Univeristy of Tasmania, Australia. The study addresses two individual research aspects. I was responsible for the bulk of the interpretation of S-isotopic data, whereas Scott Halley and Richard Tosdal supported the interpretation and figure design of the whole rock geochemical data. I was also responsible for the correlation of the two studies and their results as well as the bulk of the text, most figures, and tables. All co-authors provided technical advice and suggestions during manuscript preparation. Richard Tosdal and Thomas Bissig contributed to revisions of the manuscript. The reference for the manuscript will be as follows:  Micko, J., Halley, S., Tosdal, R.M., and Bissig, T., Whole rock and isotope geochemistry of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada: international journal to be determined.  A version of chapter 5 will be submitted for a peer-reviewed international journal. I am the primary author, whereas Shaun Barker, Greg Dipple, and Adam Kent are the co-authors. I collected the required samples and conducted most of the analytical research. Mati Raudsepp v  aided in the EMP analysis of samples and Adam Kent supported the LA-ICP-MS study. I was responsible for much of the interpretation of acquired data; however, I received significant assistance from Gregory Dipple and Shaun Barker. I designed the bulk of the text, figures, and tables. All three co-authors provided technical advice and suggestions during manuscript preparation. Greg Dipple and Shaun Barker contributed to revisions of the manuscript. The reference for the manuscript will be as follows:  Micko, J., Barker, S.L.L., Dipple, G.M., and Kent, A., Oscillatory zoning in garnets as a record for hydrothermal system evolution and brecciation in the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada: Journal to be announced.  vi  TABLE OF CONTENTS ABSTRACT……………………………………………………………………………………...ii PREFACE……………………………………………………………………………………….iv TABLE OF CONTENTS………………………………………………………………………vii LIST OF TABLES…………………………………………………………………………….xiii LIST OF FIGURES…………………………………………………………………………….xv LIST OF ABBREVIATIONS AND SYMBOLS…………………………………………....xxiv ACKNOWLEDGMENTS…………………………………………………………………....xxvi DEDICATION……………………………………………………………………………....xxviii  1  2  Introduction ........................................................................................................................... 1 1.1  Objectives ........................................................................................................................ 1  1.2  Project background and support ...................................................................................... 1  1.3  District overview ............................................................................................................. 3  1.4  Alkalic porphyry deposits ................................................................................................ 4  1.4.1  Geologic characteristics............................................................................................ 4  1.4.2  The Cadia district ..................................................................................................... 7  1.4.3  Significance for exploration ..................................................................................... 9  1.5  Previous research ........................................................................................................... 10  1.6  Overview of the dissertation .......................................................................................... 12  1.7  References...................................................................................................................... 14  Lithological description and interpretation of the host-rocks of the Central Zone  deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada ...................................................................................................................... 17 vii  2.1  Introduction.................................................................................................................... 17  2.2  Regional geology ........................................................................................................... 20  2.3  District geology ............................................................................................................. 20  2.4  Methodology .................................................................................................................. 22  2.5  Rock units of the Central Zone ...................................................................................... 24  2.5.1  Supracrustal host-rocks .......................................................................................... 24  2.5.2  The Central Zone intrusive complex (CZIC) ......................................................... 33  2.5.3  Breccia complexes .................................................................................................. 38  2.6  3  Breccia development in the Central Zone ..................................................................... 50  2.6.1  Matrix bearing breccia ............................................................................................ 50  2.6.2  Cement-bearing breccias ........................................................................................ 51  2.6.3  Mechanisms for brecciation in the CZ ................................................................... 52  2.7  Conclusions.................................................................................................................... 53  2.8  References...................................................................................................................... 54  Hydrothermal alteration and mineralization of the Central Zone deposit, Galore  Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada..... 58 3.1  Introduction.................................................................................................................... 58  3.2  Regional geology and tectonic setting ........................................................................... 62  3.3  District geology ............................................................................................................. 63  3.4  Central Zone geology .................................................................................................... 65  3.4.1  Supracrustal hostrocks ............................................................................................ 67  3.4.2  The Central Zone intrusive complex ...................................................................... 70  3.4.3  Breccias .................................................................................................................. 71  3.5  Hydrothermal alteration ................................................................................................. 73  3.5.1  Hydrothermal paragenesis of the North Gold Lens (NGL) .................................... 74 viii  3.5.2  Hydrothermal paragenesis of the Central Replacement Zone (CRZ) .................... 85  3.5.3  Hydrothermal paragenesis of the South Gold Lens (SGL) .................................... 91  3.5.4  Summary of the hydrothermal paragenesis ............................................................ 96  3.5.5  Age of Hydrothermal Alteration .......................................................................... 100  3.6  4  Discussion .................................................................................................................... 104  3.6.1  Tilting of the hydrothermal system ...................................................................... 104  3.6.2  Timing of hydrothermal alteration ....................................................................... 105  3.6.3  Hydrothermal evolution........................................................................................ 107  3.6.4  The Central zone — An end-member alkalic porphyry Cu-Au deposit ............... 114  3.7  The hydrothermal model – a summary ........................................................................ 115  3.8  References.................................................................................................................... 117  Whole rock and isotope geochemistry of the Central Zone deposit, Galore Creek  alkalic copper-gold porphyry district, northwestern British Columbia, Canada .............. 123 4.1  Introduction.................................................................................................................. 123  4.2  Geological setting ........................................................................................................ 127  4.3  Central Zone geology .................................................................................................. 128  4.3.1  North Gold Lens - geology ................................................................................... 129  4.3.2  Central Replacement Zone-geology ..................................................................... 134  4.4  Methodology ................................................................................................................ 136  4.5  Sulfur isotope distribution ........................................................................................... 139  4.5.1  North Gold Lens ................................................................................................... 141  4.5.2  Central Replacement Zone ................................................................................... 145  4.5.3  Geothermometric analysis .................................................................................... 149  4.6  Lithogeochemistry ....................................................................................................... 152  4.6.1  Variations in primary igneous chemistry ............................................................. 152 ix  5  4.6.2  Variations in immobile elements due to alteration ............................................... 159  4.6.3  Variations in alkali elements due to alteration ..................................................... 163  4.6.4  Pathfinder element distribution ............................................................................ 167  4.7  Discussion .................................................................................................................... 177  4.8  Conclusions and exploration implications ................................................................... 185  4.9  References.................................................................................................................... 188  Oscillatory zoning in garnets as a record for hydrothermal system evolution and  brecciation in the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada ................................................................. 195 5.1  Introduction.................................................................................................................. 195  5.2  Regional and local geology ......................................................................................... 198  5.3  Methodology ................................................................................................................ 199  5.4  Mineral stratigraphy..................................................................................................... 200  5.4.1  Destructive events and marker bands ................................................................... 205  5.4.2  Garnet growth zones ............................................................................................. 208  5.4.3  Petrographic summary and interpretations ........................................................... 211  5.5  6  Compositional analysis ................................................................................................ 213  5.5.1  EMP analysis ........................................................................................................ 214  5.5.2  LA-ICP-MS analysis ............................................................................................ 217  5.6  Discussion .................................................................................................................... 224  5.7  Conclusions and implication........................................................................................ 227  5.8  References.................................................................................................................... 231  Conclusions ........................................................................................................................ 235 6.1  The geology and genesis of the Central Zone deposit ................................................. 235 x  6.1.1  Host rock environment ......................................................................................... 235  6.1.2  Hydrothermal alteration and mineralization ......................................................... 237  6.1.3  Hydrothermal geochemistry ................................................................................. 239  6.1.4  Post-mineral deformation ..................................................................................... 241  6.2  Scientific significance of the dissertation .................................................................... 242  6.3  Exploration implications .............................................................................................. 245  6.4  Future research............................................................................................................. 250  6.5  References.................................................................................................................... 252  Appendix………………………………………………………………………………………255 A.1  Appendix to chapter 1………………………………………………………………..255 A1.1  A.2  Example of a diamond drill log………………….………………………………255  Appendix to chapter 3………………………………………………………………..264  A2.1 U-Th-Pb SHRIMP-RG isotopic data for hydrothermal titanite from the North Gold Lens and South Gold Lens ………………………………………………………………..264 A.3  Appendix to chapter 4……………………………………………………………...268 A.3.1 Sulfur isotope analysis of the North Gold Lens…………………………………268 A3.2  A.4  Sulfur isotope analysis of the Central Replacement Zone………………………272  Appendix to chapter 4………………………………………………………………..275 A4.1 The whole rock geochemical analysis of the Central Zone……………………..275  A.5  A.6  Appendix to chapter 5………………………………………………………………..311 A5.1  Electron microprobe analysis of garnet grain GC492-170.00m.………….……311  A5.2  Electron microprobe analysis of garnet grain GC732-297.36m………………..316  A5.3  Electron microprobe analysis of garnet grain GC733-459.50m………………..319  A5.4  Electron microprobe analysis of garnet grain GC708-556.50m..………………322  A5.5  Electron microprobe analysis of garnet grain GC738-644.00.…………………327  Appendix to chapter 6………………………………………………………………..333 xi  A6.1  LA-ICP-MS analysis GC492-170.00m…………………………………………333  A6.2  LA-ICP-MS analysis of garnet grain GC732-297.36m...………………………339  A6.3  LA-ICP-MS analysis of garnet grain GC733-459.50m...………………………343  A6.4  LA-ICP-MS analysis of garnet grain GC708-556.50m………………………...347  A6.5  LA-ICP-MS analysis of garnet grain GC738-644.00m...………………………353  xii  LIST OF TABLES Table 2.1: Summary of key terminology used in the lithological decrisption of the CZ hostrocks. Based on terminology and criteria defined by MacPhie et al. (1993) and Davies et al. (2008). .......................................................................................................................................... 24 Table 2.2: Supracrustal hostrocks - lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. .................................................................................................................... 29 Table 2.3: Galore Creek intrusive complex – lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. ................................................................................................ 35 Table 2.4: Breccia systems - lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. .......................................................................................................................... 41 Table 3.1: Hydrothermal alteration assemblages observed in the Central Zone. Both dominant and subordinate minerals were defined on the basis of macroscopic and microscopic observations backed up by SEM and EMP……………………………………………………...73 Table 4.1: Summary of the supracrustal host rocks and the CZ intrusive suite present in the NGL and CRZ section. Younger rock units such as Eocene intrusions are irrelevant to the hydrothermal system evolution and have been excluded from this summary. A detailed account of the lithologic units of the CZ can be found in Micko 2010 (thesis chapter 2). 130 Table 4.2: Suite of elements analyzed and reported detection ranges for the ALS Chemex 4-acid digestion analysis using analytical package ME-MS61m and instruments ICP-MS and ICP-AES. .................................................................................................................................................... 138 Table 4.3: Sulfur isotopic temperature estimates for sulfide-sulfide and sulafte (anhydrite)sulfide pairs from the NGL and CRZ. ........................................................................................ 150 Table 4.4: Trace element concentrations of fresh rocks of the Nicola group (Quesnell terrane) as a direct analogue to the chronologic and tectonic co-eval Stuhini group (Stikine terrane). Where specific element analyses are unavailable, average crustal contamination values werederived from Berkman (2001) and marked with (*). .............................................................................. 170 Table 5.1: Zoning protocol defining descriptive terminology used in the following text and figures. ........................................................................................................................................ 202 Table 5.2: Core to rim distribution of LA-ICP-MS derived trace element values relative to Yb/Gd. ........................................................................................................................................ 223 Table A2.1: U-Th-Pb SHRIMP-RG isotopic data for hydrothermal titanite from the North Gold Lens and South Gold Lens..........................................................................................................266 Table A.3.1: Sulfur isotope analysis of the North Gold Lens....................................................269 Table A.3.2: Sulfur isotope analysis of the Central Replacement Zone.....................................273 Table A4.1: The whole rock geochemical analysis of the Central Zone....................................276 xiii  Table A5.1: Electron microprobe analysis of garnet grain GC492-170.00m.............................312 Table A5.2: Electron microprobe analysis of garnet grain GC732-297.36m……………….....317 Table A5.3: Electron microprobe analysis of garnet grain GC733-459.50m………………….320 Table A5.4: Electron microprobe analysis of garnet grain GC708-556.50m..………………...323 Table A5.5: Electron microprobe analysis of garnet grain GC738-644.00.…………...………328 Table A6.1: LA-ICP-MS analysis of garnet grain GC492-170.00m…………………………..334 Table A6.2: LA-ICP-MS analysis of garnet grain GC732-297.36m...………………………...340 Table A6.3: LA-ICP-MS analysis of garnet grain GC733-459.50m...………………………...344 Table A6.4: LA-ICP-MS analysis of garnet grain GC708-556.50m………………………......348 Table A6.5: LA-ICP-MS analysis of garnet grain GC738-644.00m...………………………...354  xiv  LIST OF FIGURES Figure 1.1: Distribution of worldwide reknown alkalic deposits. The deposits marked in red refer to alkalic porphyry systems, whereas yellow indicates the location of epithermal systems. Study sites included in the alkalic research project are Galore Creek, Lorraine, Mt. Polley, Mt. Milligan, Porgera, Ladolam, Cadia and Cowal. . ........................................................................... 2 Figure 1.2: Schematic model of alkalic igneous complexes and associated ore deposits and alteration patterns. Redrafted from Jensen and Barton (2000). ...................................................... 5 Figure 1.3: Location of the Cadia alkalic district within the Molong Volcanic Belt of the Lachlan Fold Belt. An island arc tectonic setting is envisaged for the development of these volcanic rocks Redrafted from Wilson et al., 2007. ....................................................................... 8 Figure 2.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing location of the Galore Creek Copper porphyry Au-Cu district and other porphyry Cu centers. Black Box outlines the area shown in Fig. 2.1B. B) Regional geology of the northwestern Stikine Terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994). .......................................................................................................................... 18 Figure 2.2: Interpreted surface bedrock geology of the Central Zone showing location from three E-oriented cross-sections and one N-oriented long section that crosscut the three principal mineralized centers of the North Gold Len (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL). Also shown is the location of the deep Bountiful Zone (BZ). Geology modified after NovaGold Resources Inc. (2007). ........................................................................ 19 Figure 2.3: Regional stratigraphy and volcanic to volcaniclastic facies interpretation of the Galore Creek upper Triassic successions in the Central Zone. The blue box indicates the relative lithofacies distribution recognized in the Central Zone. Modified after Logan and Koyanagi (1994). .......................................................................................................................................... 21 Figure 2.4: Lower to upper to Triassic supracrustal host rocks in the Central Zone. A) GC0734 795.00m, and B) GC0734-811.50m show a siltstone, sandstone and ribbon chert with disseminated bornite (bn), chalcopyrite (cp), orthoclase (ortho), and biotite (bio) distributed along laminations. An anhydrite (anh) vein crosscuts the assemblage in A. C) GC0734-642.80m and D) GC0702-337.63m present a hornblende and orthoclase-phyric basaltic andesite. In C) the rock is moderately altered and crosscut by biotite veins. A granitic clast is incorporated in the groundmass and replaced by chlorite (chl), biotite, orthoclase, and pyrite (py). In D) the groundmass and orthoclase-phyric xenolith is replaced by finely, disseminated garnet, biotite, and pyrite. E) GC0702-205.33m and F) GC0573-345.63m show an Augite-phyric basalt. In E) the volcaniclastic conglomerate presents orthoclase and carbonate (carb) replaced clasts incorporated in a chlorite, biotite, and garnet replaced clastic matrix. In F) a coherent augitephyric lavaflow is shown. The groundmass is replaced by orthoclase, pyrite, and garnet, whereas the augite phenocrysts are locally affected by biotite and magnetite (mag) alteration. G) GC0573-102.20m and H) GC0448-537.50m represent the pseudoleucite-phyric trachyte and derivative rocks. G) shows a planar laminted, slightly biotite and chalcopyrite replaced pseudoleucite-phyric trachyte derived sand- and siltstone, whereas H) presents A fluidallyshaped pseudeoleucite-phyric peperite intruded into coarse sandstone. I) GC0734-588.80m and xv  J) GC0725-510.20m present the Orthoclase-phyric trachyte. The sample I) is locally replaced by anhydrite and chalcopyrite and incorporates small augite-phyric inclusions. Sample J) is derived from the SGL and represents a coherent unit replaced by biotite, chalcopyrite, and garnet. ....... 27 Figure 2.5: Upper Triassic Central Zone intrusive complex. A) GC0492-448.50m shows an orthoclase and pseudoleucite-phyric syenite. B) GC0441-370.94m is an orthoclase-phyric syenite, sub-unit (1) that contains large pseudoleucite-xenocrysts. C) GC0441-370.40m represents the same sub-unit as B), but contains abundant, mm-sized pseudoleucite-phenocrysts. D) GC0441-319.13m refers to orthoclase-phyric syenite sub-unit (3). E) GC0732-50.00m is a megacrystic orthoclase and plagioclase-phyric monzonite, subunit (1), whereas F) GC0617247.80m refers to sub-unit (3). G) GC0441-218.60m presents an orthoclase-phyric monzonite, sub-unit (1). H) GC0637-149.10m shows the same sub-unit, cementing orthoclase-phryic syenite clasts. This unit can also be referred to as monomictic orthoclase-phyric monzonite-cemented breccia........................................................................................................................................... 34 Figure 2.6: Distribution of rocks in the South Gold Lens (section 6334100). The matrix bearing breccia body contains rocks A) and B). A) GC0448-275.00m shows a fluidal, juvenile orthoclase-phyric syenite derived clast embedded in a coarse sandstone matrix, whereas B) presents a laminated sand- to siltstone clast incorporated into a sandstone to pebble-stone matrix. The cement-bearing breccia contains rocks C) and D). C) GC0637-158.50m is composed of jigsaw fit orthoclase-phyric monzonite derived clasts cemented by dentritic diopisde and anhydrite. The diopside is locally replaced by epidote (epi). D) presents the same clast type cemented by coarse biotite, magnetite, and anhydrite. ................................................................. 40 Figure 2.7: Distribution of rocks in the Central Replacement Zone (section 6335100). The cement-bearing breccia body is composed of 3 lithofacies. Litho-facies 1 CRZ 1 contains rocks A) GC0488-197.80m that shows a distinct crackle-fracture framework and void spaces. Diopside and garnet form alteration rinds to the fragments, whereas biotite forms the cement. Litho-facies CRZ 2 contains rocks B, C, and D. B) GC0732-258.00m shows angular orthoclase- and pseudoleucite-phyric clasts with a strong light brown garnet alteration rind, cemented by dark brown garnet and pyrite. C) GC0568-417.00m is a sample strongly dominated by a garnet, biotite, anhydrite, and chalcopyrite cement. D) GC0732-347.00m presents a void space lined by dentritic garnet and filled with anhydrite, chalcopyrite and pyrite. Lithofacies CRZ 3 contains rock samples E) GC0738-523.52m and F) GC0738-534.00m that are characterized by fluidal, juvenile clasts and angular, orthoclase and pseudoleucite-phyric clasts cemented by an assemblage of garnet, biotite, diopside, and magnetite. ............................................................... 47 Figure 2.8: Distribution of rocks in the North Gold Lens (section 6335547). The cement-bearing breccia body is composed of 2 lithofacies. Litho-facies NGL 1 contains rocks A) and B). A) GC0734-415.25m shows a garnet, diopside, chalcopyrite, bornite, and anhydrite cemented vein cross-cutting the coherent margin of the breccia body, whereas B) GC0501-297.00m presents a biotite and chalcopyrite cemented fractures. Litho-facies NGL=2 contains rocks C) and D). C) GC0501-318.55m shows a biotite, garnet, and chalcopyrite-replaced augite-phyric clast cemented by biotite. D) GC0501-377.60m presents a breccia sample that contains >80% hydrothermal cement (biotite, magnetite, diopside, and garnet). Only locally small clasts are visible largely replaced by garnet and magnetite. ........................................................................ 49 Figure 3.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing location of the Galore Creek Copper porphyry Au-Cu district and xvi  other porphyry Cu centers. Black Box outlines the area shown in figure 1B. B) Regional geology of the northwestern Stikine Terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994). .......................................................................................................................... 60 Figure 3.2: A) Interpreted surface bedrock geology of the Central Zone showing location from three E-oriented cross-sections and one N-oriented long section that crosscut the three principal mineralized centers of the North Gold Len (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL). Also shown is the location of the deep Bountiful Zone (BZ). Geology modified after NovaGold Resources Inc. (2007). B) Surface alteration and sulfide mineral distribution of the Central Zone. Geologic contacts in panel A reproduced as gray lines for reference. Map modified from Schwab et al. (2008)................................................................... 61 Figure 3.3: Regional stratigraphy and volcanic to volcaniclastic facies interpretation of the Galore Creek upper Triassic successions in the Central Zone. Modified after Logan and Koyanagi (1994). .......................................................................................................................... 64 Figure 3.4: Distribution of rocks in the A) North Gold Lens (section 6335547), B) Central Replacement Zone (section 6335100); and C) the South Gold Lens (section 6334100). Section location is in figure 3.2A. ............................................................................................................. 66 Figure 3.5: Distribution of rocks along a vertical N-oriented long section 351000 through the three mineralized zones composing the Central Zone. Section location is in figure 3.2A. .......... 67 Figure 3.6: Late Triassic Stuhini Group and intrusive units in the Central Zone. A) Lower to middle Triassic phyllite and ribbon chert with disseminated bornite and chalcopyrite distributed along laminations; GC06-0734 (795.00m), NGL, potassic 2a. B) Augite-phyric basaltic conglomerate; GC05-0702 (205.33m), NGL, potassic and calcic 2b. C) Fluidally-shaped pseudoleucite-phyric clasts in volcaniclastic sandstone (peperite); pseudoleucite phenocrysts are locally replaced by biotite, chalcopyrite and pyrite; GC04-0448 (537.50m), SGL, potassic 1 and 2a. D) Orthoclase-phyric trachyte (subvolcanic intrusion); GC05-0734 (590.00m), NGL, potassic 2a. E) Orthoclase and pseudoleucite-phyric syenite crosscut by a garnet and chalcopyrite vein; GC06-0732 (297.36m), potassic 2a and calcic 2b. F) Orthoclase-phyric syenite; GC03-0441 (319.13m), SGL, potassic 3a. G) Megacrystic orthoclase and plagioclasephyric monzonite locally replaced by late garnet; GC05-0537 (395.45m), NGL, potassic 2d and calcic 4b. H) Orthoclase-phyric monzonite crosscut by microfractures with orthoclase (or) selvages; GC06-0721 (277.70m), SGL, potassic 3a. I) Polymictic rock flour matrix breccia (SGL); GC04-0448 (275.00m), potassic 2a. J) Polylithic, pyroxene-anhydrite-cemented breccia (SGL); GC06-0721 (158.60m), calcic 3b and propylitic 4d. Mineral abbreviations: an, anhydrite; aug, augite; cpy, chalcopyrite; dp, diopside; epi, epidote; gar, garnet; or, orthoclase; ps, pseudoleucite; py, pyrite. ........................................................................................................ 68 Figure 3.7: Hydrothermal alteration stages and associated textures in the Central Zone. Galore Creek is a silica-undersaturated magmatic-hydrothermal system and thus lacks (quartz-) veins and stockwork development. Where crosscutting relationships between individual alteration assemblages have been observed photographic evidence is provided in this figure. Several alteration stages, however, were defined on the basis of crosscutting and timing relationships between rock units, i.e intrusions and breccias. The presence or absence of a specific alteraration assemblage in one unit provides a relative paragenetic sequence despite the lack of distinct overprinting relationships. The reader is thus refered to section 3.4 and chapter 2, Tables 2.2 to xvii  2.4. A) Fresh orthoclase-phyric trachyte crosscut by orthoclase-bearing veins of potassic (pot) stage 1; GC05-0568 (179.50m), NGL B) Orthoclase-phyric trachyte pervasively altered by texturally non-destructive orthoclase of potassic stage 1, crosscut by biotite and magnetitebearing veins of potassic stage 2a; GC06-734 (367.00m), NGL. C) Pseudoleucite-phyric syenite pervasively altered by orthoclase of potassic stage 1, crosscut by biotite and chalcopyrite-bearing veins of potassic stage 2a. Pseudoleucite phenocrysts are replaced by biotite and chalcopyrite preserving the original crystal shape; GC05-0514 (238.50m), NGL. D) CRZ breccia: Pseudoleucite-phyric syenite derived clast pervasively altered by potassic stages 1 and 2, cemented by garnet, biotite and anhydrite of calc-potassic (calc-pot) stage 2b; GC06-0732 (294.00m), CRZ. E) Orthoclase-phyric trachyte replaced by texturally non-destructive orthoclase of potassic stage 1, overprinted by orthoclase and biotite-bearing alteration of potassic stage 2a, crosscut by coarse, pegmatitic orthoclase and biotite bearing vein of potassic stage 2c; GC060734 (363.70m), NGL. F) Hornblende and plagioclase-phyric basaltic andesite replaced by finely disseminated diopside, biotite and magnetite of calc-potassic stage 2b, crosscut by coarse, pegmatitic orthoclase, biotiten and anhydrite bearing vein of potassic stage 2c; GC06-0734 (314.00m), NGL.) G) Megacrystic orthoclase and plagioclase-phyric monzonite is crosscut and pervasively altered by texturally destructive orthoclase of potassic stage 2d; GC05-0637 (469.00m), SGL. H) SGL breccia: Orthoclase-phyric monzonite clasts pervasively altered by texturally non-destructive orthoclase and minor biotite of potassic stage 3a and cemented by diopside and anhydrite of calcic stage 3b; GC05-0637 (158.60m), SGL. I) SGL breccia: Orthoclase-phyric trachyte derived clasts replaced by several stages of potassic alteration and cemented by magnetite and biotite of potassic stage 3b; GC05-0637 (159.50m), SGL J) SGL breccia cemented by alteration assemblages of calc-potassic stage 3b overprinted by pervasive, texturally destructive orthoclase of potassic stage 3c and crosscut by siderite (sid) vein of propylitic stage 4d; GC05-0637 (216.15m), SGL. K) Orthoclase-phyric syenite replaced by texturally destructive albite (alb) alteration. Chalcopyrite and bornite may have been deposited prior to or syn-sodic alteration; GC06-0721 (447.40m), SGL. L) Megacrystic orthoclase and plagioclase-phyric monzonite pervasively altered by texturally non-destructive orthoclase and biotite of potassic stage 2d as well as small accumulations of garner of calcic stage 4b; GC050637 (395.45m), SGL. M) Unknown hostrock in the vicinity of the South Fault, texturally obliterated by coarse crystalline orthoclase and overprinted by sericite (ser) that is composed of white muscovite (mus) and fuchsite (fuch) associated with Sericite-Anhydrite-Carbonate (SAC) alteration stage 4c; GC05-0637 (398.40m), SGL. N) Augite-phyric basalt crosscut by sericite and calcite-vein of SAC stage 4c and overprinted by pervasive chlorite alteration of propylitic stage 4d; GC05-0702 (267.10m), NGL………………………………………………………….74 Figure 3.8: Distribution of alteration mineral assemblages in the CZ along the vertical long section 351000. View represents an oblique cut through the eastward tilted hydrothermal systems. A) Orthoclase and specular hematite distribution; B) biotite and magnetite distribution; C) calcic alteration; D) SAC and propylitic alteration assemblages. ........................................... 78 Figure 3.9: A) Sulfide and alteration assemblage distribution and B) metal zonation of the CZ along the vertical long section 351000. View represents an oblique cut through the eastward tilted hydrothermal systems. ......................................................................................................... 79 Figure 3.10: Distribution maps of the four alteration types and associated assemblages in the NGL along section 6335547 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration xviii  assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.0-2.0 g/t Au). ............................................................................................................................................... 80 Figure 3.11: Distribution maps of the four alteration types and associated assemblages in the CRZ along section 6335100 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.0-2.0 g/t Au). ............................................................................................................................................... 88 Figure 3.12: Distribution maps of the five alteration types and associated assemblages in the South Gold Lens along section 6334100 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) Sodic, SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.0-2.0 g/t Au). Evidence for the deeper Bountiful Zone is present in the deeper eastern parts of the section. .......................................................................................................... 93 Figure 3.13: Paragenetic summary of hydrothermal alteration and mineralization events within the three mineralized centers of the Central Zone. Note that the timing and intensity of events varies between the three centers…………………………………………………………………99 Figure 3.14: Hydrothermal titanite samples for U-Pb SHRIMP-RG analysis. A) South Gold Lens: coarse hydrothermal titanite intergrown with diopsidic pyroxene and anhydrite of calcic 2b stage (GC0495-227.46m) B) North Gold Lens: hydrothermal titanite of potassic 2c stage (GC0734-350.50m) derived from a coarse, pegmatitic orthoclase, biotite and titanite bearing vein (Fig. 3.7E)…………………………………………………………………………………100 Figure 3.15: U-Pb Tera-Wasserburg concordia diagrams and weighted mean histograms for titanites from the CZ, Galore Creek, British Columbia. A) South Gold Lens; B) NGL; grey boxes in histogram are from the non-magnetic titanite whereas black boxes are for magnetic titanite. ........................................................................................................................................ 103 Figure 3.16: The geological and hydrothermal evolution of the CZ. Main stage (1): Formation of one or multiple potassic alteration cells and mineralization in the Central Zone with emphasis on the NGL and SGL. Emplacement of a hydrothermal breccia body in the CRZ. Hydrothermal cementation lead to widespread calc-potassic alteration and mineralization. Main stage (2): Monzonite intrusion followed by emplacement of a hydrothermal breccia body in the SGL and potentially the development of the South Faults. Hydrothermal cementation leads to widespread calc-potassic alteration and minor mineralization. Late stage: Intrusive activity and brecciation ceased in the CZ. Onset of the waning stage of the hydrothermal system and development of a sodic alteration assemblage in the SGL and a widespread propylitic, calcic alteration assemblage due to the mixing of unknown fluids with magmatic discharge. ............................................... 112  xix  Figure 4.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing the location of the Galore Creek Cu-Au porphyry district and other porphyry Cu centers. B) Regional geology of the northwestern Stikine terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994). ...................................................... 125 Figure 4.2: A) Interpreted surface bedrock geology of the Central Zone showing the location of three E-oriented cross-sections that crosscut the principal mineralized centers, the North Gold Lens (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL), of which the NGL and CRZ are the foci for this study. The geology is modified after NovaGold Resources Inc. (2007). B) Surface alteration and sulfide mineral distribution of the Central Zone, modified from Schwab et al. (2008). ......................................................................................................... 126 Figure 4.3: A) Distribution of lithologic units in the NGL cross-section (6335550). B) Hydrothermal alteration assemblages and sulfide mineral distribution in the NGL cross-section. .................................................................................................................................................... 132 Figure 4.4: A) Distribution of lithologic units in the CRZ cross-section (6335100). B) Hydrothermal alteration assemblages and sulfide mineral distribution in the CRZ. The geologic key for this figure can be found in Fig. 4.3. ............................................................................... 134 Figure 4.5: Schematic presentation of sulfur isotope data of alkalic and calc-alkalic porphyry deposits worldwide. Modified after Barnes (1979) and Ohmoto and Rye (1979). Additional data concerning alkali porphyry deposits with the exception of Galore Creek are derived from Wolfe (1994), Heithersay and Walshe (1995), Harper (2000), Wolfe (2001), Lickfold (2002), Harris and Golding (2002), Lickfold et al. (2003), Wilson (2003), Wilson et al. (2003), Deyell and Tosdal (2005), Reese et al. (2005), Wilson et al. (2007a), Pass, (2010), Bath and Cooke (2008). .................................................................................................................................................... 140 Figure 4.6: Examplatory sulfide and sulfate samples of the NGL and CRZ in thin section (to the left) and hand sample (to the right). A) GC04-0501 (487.50m) is representative of the potassic stage 2a sulfide+sulfate mineral assemblage that consists of texturally in equilibrium chalcopyrite, bornite and anhydrite with minor magnetite. B) GC06-0732 (296.70m) shows a large amalgamation of in equilibrium pyrite and chalcopyrite with anhydride common for the calc-potassic alteration stage 2b. ………………………………………………………………142 Figure 4.7: A) Contoured values of δ34S (‰) of sulfides and sulfates derived from the early main stage potassic alteration assemblage in the NGL. B) Contoured values of δ34S (‰) of sulfides and sulfates derived from the later main stage calc-potassic alteration assemblage in the NGL. C) Au+Cu grades and sulfide distribution, overlapped by overall potassic and calcpotassic mineralization derived δ34S (‰) contours. ................................................................... 143 Figure 4.8: Distribution of Cu (wt%) and Au (g/t) concentration relative to δ34S (‰) values both in sulfide and sulfate samples. Note that the dominant number of samples associated with high metal values fall into a δ34S range of -10 to -5‰ for sulfides and +4 to +7‰ for sulfates (highlighted in grey).. ................................................................................................................. 145 Figure 4.9: A) Contoured values of δ34S (‰) of sulfides and sulfates derived from the early main stage potassic alteration assemblage in the CRZ. B) Contoured values of δ34S (‰) of sulfides and sulfates derived from the later main stage calc-potassic alteration assemblage in the xx  CRZ. C) Au+Cu grades and sulfide distribution, overlapped by overall potassic and calc-potassic mineralization derived δ34S (‰) contours. ................................................................................. 147 Figure 4.10: Plot of δ34S (‰) values for associated sulfate (anhydrite) and sulfide minerals pairs versus the Δ value of the pairs. The convergence of the slopes of the two regression lines offers an approximation of the bulk sulfur isotopic composition (δ34SƩS) and the proportions of oxidized to reduced sulfur (XSO42- to XH2S) in the hydrothermal system (after Fields et al., 2005). .......................................................................................................................................... 152 Figure 4.11: Harker variation diagrams identifying the SiO2 (wt%) versus Ti, Y, Th, Nb, and Zr (ppm) concentrations and potential igneous fractionation paths. See inserted key for colour and symbol code. ............................................................................................................................... 154 Figure 4.12: Sc (ppm) versus Ti (wt%), Y, Th, Nb, and Zr (ppm) scatterplots mafic and felsic to intermediate composition in host rocks and hydrothermal affinities. See inserted key for colour and symbol code. ........................................................................................................................ 157 Figure 4.13: Sc (ppm) versus (A) Ti (wt%), (B) Fe and (C) V (ppm) - scatterplots differentiate between primary magmatic, hydrothermal affinities and degree of oxidation of host rocks. Note that hydrothermal breccia and MET samples have been added to the dataset. .......................... 160 Figure 4.14: A) Molar ternary K-Al-Ca and (B) molar K-Al-Ca ratio plot identifying the projected mineralogy of lithologic units as well as potential fractionation trends. C) Molar ternary K-Al-Ca and (D) molar K-Al-Ca ratio plot identifying the dominant hydrothermal mineral assemblages with the help of element ratio tie lines. See inserted key for colour and symbol code. ............................................................................................................................... 164 Figure 4.15: Attribute map identifying the distribution of the four main minerals assemblages defined by the molar K-Al-Ca ternary and ratio plot on the combined cross-section of the NGL and CRZ. The outline of the NGL cross-section is depicted in grey and spatially set behind the CRZ highlighted in black. See inserted key for the colour and symbol code. ........................... 167 Figure 4.16: Probability plots based on the N-Score distribution of pathfinder elements in correlation with the four main mineral assemblages identified in the molar K-Al-Ca ternary and ratio plots above. The common crustal contamination value or background level of each pathfinder element is indicated in the upper left corner of each N-score plot. These values are more specifically defined in table 2............................................................................................ 169 Figure 4.17: Distribution of pathfinder elements associated with group 1 (V, Cu, S, and Se) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, whereas the footprint of highest values is shown in red. See inserted key for the remaining colour code. ................................................................................................................................ 172 Figure 4.18: Distribution of pathfinder elements associated with group 2 (Te, Bi, and As) and group 3 (Li) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, whereas the footprint of highest values for group 2 is shown in green and for group 3 is shown in blue. See inserted key for the remaining colour code. ............................... 174 Figure 4.19: Distribution of pathfinder elements associated with group 3 (Tl) and 4 (Sb) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, xxi  whereas the footprint of highest values for group 3 is shown in blue and for group 4 is shown in yellow. See inserted key for the remaining colour code. ........................................................... 176 Figure 4.20: Log fO2 – log H2 versus pH diagram at 300°C showing the stability fields of Feoxides and sulfides (blue), K-felspar and muscovite (pink), aqueous sulfur-bearing species (dotted black line), gold solubility contours (grey to orange), and the predominance fields of Au(HS)2-, AuHS, and AuCl2- (green). The pink ellipse represents the estimated fluid composition during early main stage potassic mineralization event, whereas the brown one represents the later main stage calc-potassic mineralization event. Modified after Tunks (1996) and Cooke and Simmons (2000). ............................................................................................... 180 Figure 4.21: A) Combined cross-section of the NGL and CRZ showing the spatial distribution of all pathfinder element groups‘ footprints and potential direction of hydrothermal fluid flow. B) Conceptual sketch showing palaeo-vertical fluid flow, pathfinder element distribution and mineralization along Redox gradients indicated by lithologic boundaries. C) Vanadium (>700 ppm) and Arnsenic (>20 ppm) footprints shown in relation to sulfide and grade distribution in the NGL and CRZ. ..................................................................................................................... 184 Figure 5.1: A) Location of the Galore Creek Cu-Au porphyry district in northwestern British Columbia. Galore Creek is situated within the Stikine terrane, whereas most of B.C.‘s alkalic porphyry deposits are distributed in NW-SE orientation along the Quesnell terrane. B) Plan map of the Central Zone‘s interpreted geology derived from three E-W oriented cross-sections and one N-oriented longsection (modified after NovaGold Resources Inc., 2007; Micko et al., in review; chapter 3). ...................................................................................................................... 197 Figure 5.2: In order to provide a better indicator on the palaeo-vertical orientation of the garnet samples in respect to the calcic alteration zone and associated breccia body, the E-W-oriented cross-section through the CRZ (see Fig. 5.1) was rotated 45ºW. A) Lithological units of the CRZ and sample locations. B) Calcic alteration assemblage and sulphide distribution; A and B are modified after Micko et al. (in review; chapter 3)...................................................................... 201 Figure 5.3: Stratigraphic representation of selected garnet grains of the CRZ, levelled on marker band ―M1‖. Each column shows an accurate representation of the individual crystal‘s morphology. In order to confirm the consistent recurrence of morphological features, several grains from one sample location were examined. Due to the extensive dataset acquired, only one zoning profile per garnet grain is portrayed, with the exception of GC06-0738-644.00m grains 1 and 2. See inserted key for colour and symbol code. ................................................................. 204 Figure 5.4: Textural evidence for frequent chemical dissolution and mechanical fracturing of garnet grains. A) GC733-459.50m: well developed regular growth bands are heavily truncated by dissolution surface D1. B) GC738-644.00m: D1+M1 preserve and highlight a small section of a previous growth band. C) GC492-170.20m: D3 crosscuts D2+M2 in several places. D) GC708-556.60m: Fracture event coeval with D4 crosscutting previous cement garnet and sealed with M4 garnet. E) GC733-480.47m: Fracture associated with D2 infilled by M2. F) GC492141.50m: Example of subtle, hummocky dissolution surface D4 in the outer growth zone. ..... 200 Figure 5.5: A-C) Examples of cement and replacement garnets in hand sample. D-G) Representation of garnets‘ inner, medial, and outer growth zones in thin section, summarized by xxii  a conceptual sketch of the average garnet grain, its zone specific textures, associated dissolution/fracture horizons and marker bands. ........................................................................ 203 Figure 5.6: A-E) Representative garnet grains showing (1) numbered EMP and laser ablation points analyzed along ‗core to rim‘-traverses as well as (2) dissolution and fracture horizons. Each analytical point is colour-coded according to its location within the inner, medial, and outer growth zone, as well as individual marker bands. ...................................................................... 214 Figure 5.7: Triplots presenting the major element composition of representative garnet grains expressed in mol%. The formulae are calculated for 12O. Fe3+ is assumed dominant in the hydrothermal system and no additional calculations were attempted in order to differentiate between ferric and ferrous iron content. ..................................................................................... 215 Figure 5.8: Weight% oxide vs. time (core to rim traverse) plots, demonstrating the distinctive antithetic behaviour of Al vs. Fe3++Ti, particularly during events of marker band precipitation. .................................................................................................................................................... 217 Figure 5.9: Chondrite normalized REE diagrams of representative garnet grains (McDonough and Sun, 1995). Again, each analytical series has been colour-coded in respect to location (compare Fig. 5.6). ..................................................................................................................... 220 Figure 5.10: Linear (A) and log (B) scale Pr/Gd vs. Yb/Gd plots. Each analytical point is chondrite normalized and has been colour-coded in respect to location as demonstrated in Figs. 5.6 and 5.9. ................................................................................................................................. 221 Figure 5.11: Trace element vs. core to rim traverse (i.e. time) plots of two representative garnet grains showing the sympathetic and antithetic behaviour of trace elements in respect to Yb/Gd (Table 2). All ‗trace element vs. time‘ curves are calculated from raw LA-ICP-MS data, whereas the Yb/Gd ratio is based on chondrite normalized values. ......................................................... 222 Figure 5.12: Spatial distribution (deep to shallow) of Eu/Eu* along the palaeo-vertical axes of the CRZ‘s breccia body. All data points are representative of the garnets growth without marker bands. .......................................................................................................................................... 223 Figure 5.13: Conceptual summary sketch of the physicochemical development of the CRZ‘ hydrothermal breccia body. A) The introduction of magmatic fluids derived from an underlying batholiths and discharged via fingering intrusions led to the hydrothermal brecciation in the shallow crust (1-3km) abd subsequent garnet cementation. B) Continuous influx of highly oxidized corrosive fluids resulted in several cycles of permeability creation and destruction. Mechanical fracturing and chemical dissolution events were thus introduced that left a physicochemical fingerprint in fractures, dissolution horizons and marker bands. C) The interaction of reduced wall-rocks and clasts with oxidized fluids led to the development of a redox gradient between the deep base and shallow apex of the breccia body. Therefore, the apex of the breccia body became a trap for sulfide mineralization. ................................................... 230 Figure A1.1: Example of a diamond drill log…………………………………………………256  xxiii  LIST OF ABBREVIATIONS AND SYMBOLS BCGS - British Columbia Geological Survey CDT - Canyon Diablo Troilite CIC - Cadia Intrusive Complex CODES - Council Centre Of Excellence In Ore Deposits CRZ - Central Replacement Zone CZ - Central Zone Deposit CZIC - Central Zone Intrusive Complex D - Dissolution Event EMP - Electron Microprobe GSC - Geological Survey Of Canada HFSE - High Field Strength Element HREE - Heavy Rare Earth Elements ICP-AES - Inductively Coupled Plasma-Atomic Emission Spectronometer LA-ICP-MS - Laser Ablation Inductively Coupled Plasma-Mass Spectronometer LOI - Loss On Ignition LREE - Light Rare Earth Elements M - Marker Band xxiv  MDRU - Mineral Deposit Research Unit MET - Metallurgical Sampling/Sample MSWD - Mean Square Weighted Deviation NGL - North Gold Lens PCIGR - Pacific Center For Isotopic And Geochemical Research PGE - Platinum Group Elements SAC - Sericite-Anhydrite-Carbonate Alteration SEM - Scanning Electron Microscope SGL - South Gold Lens SHRIMP-RG - Sensitive High Resolution Ion Micro Probe-Reverse Geometry REE - Rare Earth Element XPL - Cross Polarized Light  xxv  ACKNOWLEDGEMENTS This work forms part of a larger MDRU-CODES research project investigating shallow and deep-level alkalic deposits in collaboration with the GSC. Funding and field support was provided by Amarc Resources, Anglogold-Ashanti, Barrick Gold Corp., Imperial Metals Corp., Lysander Minerals Corp., Newcrest Mining Ltd., Newmont Mining Corp., NovaGold Resources Inc., Teck Ltd., NSERC CDR and Geoscience BC. Logistical and field support from Terrane Metals Corp., Eastfields Resources Ltd. and Lihir Gold Mine is also acknowledged. Additional funds for this Galore Creek project were also provided through SEG student research grants and Geoscience BC scholarships. I would like to thank Novagold Resources Inc. for their financial support of the project. Special thanks are owed to Scott Petsel, Stuart Morris, Danette Schwab, and Erin Workman, as well as the remaining staff members of the Galore Creek Exploration Team of 2006 and 2007. I offer my gratitude to Dr. Richard Tosdal, Dr. Gregory Dipple, Dr. Thomas Bissig, Dr. Claire Chamberlain and Dr. Kirstie Simpson for their guidance and supervision throughout this project. I would like to express further thanks to Dr. Mati Raudsepp for direction in the use of SEM and microprobe, Dr. Shaun Barker for his valuable support in the analysis of garnets, Dr. Adam Kent and Allison Koleszar for the introduction to LA-ICPMS analysis and Dr. Bruno Kieffer for assistance with Sr isotope analyses at the Pacific Center for Isotope and Geochemical Research (PCIGR), as well as Arne Toma (MDRU resource centre coordinator), Karie Smith, and Manjit Dosanjh (MDRU accountants) for office assistance. Special thanks are owed to Prof. David Cooke and Dr. Anthony Harris of the Centre of Excellence in Ore Deposits (CODES) at the University of Tasmania for their support throughout this project. Special thanks are also offered to the great team of students of the alkalic research  xxvi  group. They include my partner in the field Kevin Byrne, as well as Meghan Jackson, Amber Henry, Paul Jago, Jacqueline Blackwell, Heidi Pass, Wojtek Zukowski, and Adam Bath.  xxvii  DEDICATION This work is dedicated to my loving family in Germany, in particular my father Dieter, mother Sabine, and sister Jessica. It is also dedicated to my wonderful partner in life Frazer, my new found family the Elliotts & Winslows, as well as my dearest friends in Canada, Tashia Dzikowski, Selina Wu Gregory, and Crystal Yarham. Thank you for your endless support and encouragement.  ―SAPERE AUDE… …DARE TO KNOW‖ (Horace, epistulae 1,2,40)  xxviii  1  Introduction  1.1 Objectives In recent years, worldwide discoveries have raised awareness of the economic importance of alkalic Cu-Au porphyry systems. They have been found to contain high tonnage, low grade ore concentrations that equal and even exceed combined resources of many of their calc-alkalic cousins. Despite their economic significance, the deposit type remains poorly understood and data derived from well described mineral provinces varies markedly. This dissertation is a case study of the Central Zone alkalic Cu-Au porphyry deposit, located in the late Triassic Galore Creek district, northwestern British Columbia. The Central Zone Cu-Au deposit is the largest of the known resources at Galore Creek and represents the end-member of the silica-undersaturated alkalic porphyry systems. Thus, provides an excellent opportunity to enhance the understanding of this deposit type. In order to fully comprehend the hydrothermal genesis of Galore Creek’s Central Zone deposit, a detailed investigation of the lithological and dominant hydrothermal characteristics was necessary. Deposit-scale geological features linked with geochemical analysis constrain the deposit’s hydrothermal evolution, as well as its mineral and metal zonations, and provide implications for exploration.  1.2 Project background and support This Ph.D. study is part of the “Alkalic Research Project” undertaken by the Mineral Deposit Research Unit (MDRU) and the Australian Research Council Centre of Excellence in Ore Deposits (CODES). This three year, industry supported, multidisciplinary project aimed to 1  advance the understanding of alkalic hydrothermal systems and to subsequently develop a holistic model for alkalic epithermal and porphyry environments. The overall study focused on seven deposits dominantly located in known alkalic magmatic provinces within the Stikine and Quesnel Terranes of British Columbia, Canada, as well as the Lachlan Fold Belt, New South Wales, Australia (Fig. 1.1).  Figure 1.1: Distribution of worldwide reknown alkalic deposits. The deposits marked in red refer to alkalic porphyry systems, whereas yellow indicates the location of epithermal systems. Study sites included in the alkalic research project are Galore Creek, Lorraine, Mt. Polley, Mt. Milligan, Porgera, Ladolam, Cadia and Cowal.  The Alkalic Research Project was supported by Amarc Resources, Anglogold-Ashanti, Barrick Gold Corp., Imperial Metals Corp., Lysander Minerals Corp., Newcrest Mining Ltd., Newmont Mining Corp., NovaGold Resources Inc., Teck Ltd. and Geoscience B.C. Direct financial and logistic support for the Galore Creek Project was provided by NovaGold Resources Incorporated. Other financial resources were academic grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and scholarships provided by the Society of Economic Geologists (SEG) and Geoscience BC.  2  1.3 District overview The Galore Creek alkalic Cu-Au porphyry district is located about 100 km northeast of Wrangell, Alaska. The district was initially discovered by an aero-magnetic survey in the late 1950s. Since the early 1960s the district has been explored by various companies including Stikine Copper Ltd., Kennecott and most recently NovaGold Resources Inc. Since 2007, the Galore Creek Mining Cooperation, an equal partner joint venture between NovaGold Resources Inc. and Teck Resources Ltd., operates the property. The district contains five explored prospects and six other mineralized centers with only limited exploration. The prospects define a five kilometer long, northwesterly trending corridor. The largest prospect at Galore Creek is the Central Zone, the focus of this dissertation. It contains three adjacent and overlapping mineralized centers: the North Gold Lens, the Central Replacement Zone and the South Gold Lens. In 2008, the combined measured and indicated resources at Galore Creek are 785.7 million tonnes grading at 0.52% Cu, 0.29g/t Au and 4.87g/t Ag (NovaGold Resources Inc., 2010). Galore Creek is one of a number of alkalic Cu-Au porphyry districts developed in the Upper Triassic to Lower Jurassic volcano-plutonic-arc rocks of the Quesnell-Stikine arc (Barr et al., 1976; Nelson and Mihalynuk, 2004). Similar deposit types are scattered along the length of the Quesnel arc in the Intermontane Belt associated with the Iron Mask Batholith and the Copper Mountain Intrusions to the south and the Hogem Batholith to the north (Logan, 2004), and correlative rocks in the Stikine terrane on the northwest (Galore Creek, Shaft Creek). The late Triassic Galore Creek alkalic Cu-Au porphyry district lies in the Stikine terrane along the western margin of the Intermontane Belt about 7 km east of the Coast Plutonic Complex (Allen et al., 1976). Tectono-stratigraphic elements of the Stikine Terrain include the Late Palaezoic to Middle Jurassic island arc volcanic and sedimentary rocks of the Stikine assemblage, the Stuhini Group and the Hazelton Group. In addition, they comprise the Middle Jurassic to early Late Cretaceous basinal sedimentary rocks of the Bowser Lake Group, as well as Late Cretaceous to 3  Tertiary continental arc volcanic assemblages of the Sloko Group, and the Late Tertiary to Recent post-orogenic plateau basalt of the Edziza and Spectrum Ranges (Enns et al., 1995). The Stikine assemblage forms the basement of the Stikine terrane (Enns et al., 1995). It consists of a sequence of Devonian to Permian mafic and intermediate flow and volcaniclastic units, interbedded with carbonate, minor shale, as well as beds of chert (Monger, 1977). Extensive units of Mississippian and Permian carbonate are exposed northeast of Galore Creek (Enns et al., 1995). Rocks of the Upper Stuhini Group can include a variety of green and maroon volcanic rocks, breccias and sedimentary rocks that unconformably overlie the Stikine assemblage (Enns et al., 1995). Panteleyev (1976) subdivided the volcanic rocks at Galore Creek into a lower unit of submarine augite-phyric basaltic to andesitic flows and breccias typical for the Stuhini Group, and an upper unit of partially subaerial, compositionally distinct alkalienriched flows and pyroclastic rocks (Enns et al., 1995). Radiometric dates by Anderson (1984) and fossil ages by Souther (1972) indicate ages for the Stuhini Group that range from early Carnian to late Norian (Enns et al., 1995). Rocks equivalent to the lower Jurassic Hazelton Group are recognized to the North of the Galore Creek area (Logan, 1989).  1.4 Alkalic porphyry deposits 1.4.1  Geologic characteristics  Jensen and Barton (2000) provide the most comprehensive review of this deposit style for both shallow and deep-level alkalic igneous settings (Fig. 1.2). They identify a number of characteristics of alkalic porphyry deposits on a regional scale. The Galore Creek deposit exhibits most of them.  4  Figure 1.2: Schematic model of alkalic igneous complexes and associated ore deposits and alteration patterns. Redrafted from Jensen and Barton (2000).    Alkaline rocks associated with Au-deposition are commonly found in arc environments and areas of extensional tectonics.    Intense K-metasomatism leads to the development of a large potassic alteration footprint commonly surrounded by an extensive propylitic aureole (e.g. Galore Creek: Lang et al 1995; Mount Polley; Fraser et al., 1995).    The deepest parts of some systems can be associated with a calc-silicate assemblage, commonly accompanied by sodic alteration (Jensen and Barton, 2000). Sodic alteration has 5  also been recognized peripheral to potassic zones (Cadia East, NSW, Australia; Wilson et al., 2007).   Hydrothermal quartz is less prominent in contrast to calc-alkalic systems and, in some hightemperature alkalic deposits, even absent (Jensen and Barton, 2000). Alkalic deposits of BC, including Galore Creek, Mount Polley and Lorraine, represent type-localities for this feature.    Advanced argillic and phyllic alteration tends to be weakly developed. Both hydrolytic alteration types tend to occur late in the hydrothermal system and are typically restricted to fault-zones (Cooke et al., 2002). Sericite in association with carbonate is common.    Wallrock alteration is usually represented by a biotite-magnetite-orthoclase assemblage. The abundance of biotite and magnetite is controlled by the Fe and Mg content of the wall rocks.    Skarns may occur and can be economically significant. Potassic style alteration in igneous rocks tends to correlate with calc-potassic assemblages in altered carbonate rocks dominated by andraditic garnets, diopside, epidote and sometimes biotite.    Breccias in alkalic systems are associated with hydrothermal and phreatomagmatic processes. Magnetite-cemented hydrothermal breccias are of particular importance as they may host high grade ore (Cooke et al., 2007).    Styles of mineralization can range from disseminated to stockwork-veined ore. Au may be present as discrete grains of native gold, tellurides, or auriferous sulfides. Alkalic porphyry deposits may also show elevated Te and PGE concentrations (Werle et al., 1984; Saunders, 1991).    In Cu-rich deposits, Au is commonly associated with bornite and high copper concentration. Au is usually found in stockwork veins of quartz, sulfides, molybdenite, native gold and tellurides. 6  1.4.2  The Cadia district  The largest of the known alkalic porphyry districts to date is Cadia, New South Wales, Australia. Discovered by Newcrest Mining Ltd. in 1992, pre-mine resources of the district were in excess of 585 tonnes of Au and 2.35 million tonnes of Cu (Holliday et al., 2003). Located in the late Ordovician Molong Volcanic Belt in the eastern Lachlan Fold Belt (Holliday et al., 2003) the Cadia district combines a number of Au-Cu-bearing deposits such as Ridgeway, Cadia Hill, Cadia Quarry, Cadia East, Little and Big Cadia (skarns). In particular, Cadia East represents a good example for an alkalic porphyry system that comprises several distinctive characteristics described in Jensen’s and Barton (2000) and, thus, also shows similarities to Galore Creek in terms of mineralization and hydrothermal alteration style (Fig. 1.3).  7  Figure 1.3: Location of the Cadia alkalic district within the Molong Volcanic Belt of the Lachlan Fold Belt. An island arc tectonic setting is envisaged for the development of these volcanic rocks Redrafted from Wilson et al., 2007.  The Cadia East alkalic porphyry deposit contains an inferred resource as of 830 million tonnes at 0.69 g/t Au and 0.35% Cu (Wilson et al., 2007). The mineralization is both vein affiliated as well as disseminated and occurs broadly stratabound within volcaniclastic conglomerates and sandstones of the Forest Reefs Volcanics. Subjacent to this, higher grade AuCu mineralization has been recognized within and around a series of quartz-monzonite porphyry dykes referred to as Cadia Intrusive Complex (CIC; Wilson et al., 2007). The close spatial association between gold and copper mineralization and the shoshonitic, monzonitic CIC at Cadia East argues strongly for a genetic link between the two (Holliday et al., 2003) and the 8  same argument has been applied at Galore Creek. As at Galore Creek, sulfide mineralization is strongly zoned with bornite-rich (Au bearing) cores surrounded by chalcopyrite-rich halos and peripheral zones of pyrite mineralization (Wilson et al., 2007). Hydrothermal breccias are absent at Cadia. The hydrothermal paragenesis at Cadia East is similar to the Central Zone of Galore Creek as it is characterized by numerous potassic alteration stages. Thus, a large potassic footprint is created that proves problematic in the exact location of high grade ore. Early stage biotite-orthoclase-magnetite alteration (Potassic I) has been cut by sheeted, main stage quartzcalcite-sulfide veins associated with orthoclase alteration envelopes (Potassic II; Wilson et al., 2007). At shallower depths, stratabound mineralization comprises disseminated chalcopyritepyrite associated with pervasive biotite ± tourmaline alteration (Potassic III; Wilson et al., 2007). A subzone of pink hematite-bearing propylitic alteration (inner propylitic) occurs between potassic alteration zones and the peripheral sub-zone of propylitic alteration (Wilson et al., 2007). In the upper levels of the deposit, all stages of potassic alteration are overprinted by zones of late stage pervasive feldspar alteration characterized by white potassium feldspar, albite and locally abundant pyrite (Wilson et al., 2007). Fracture and fault controlled phyllic alteration has locally overprinted all of the earlier formed alteration assemblages (Wilson et al., 2007). Calcic alteration stages common in the Galore Creek district have not been reported at Cadia. 1.4.3  Significance for exploration  Recognizing the general characteristics described by Jensen and Barton (2000) has aided in regional scale prospecting for alkalic porphyry deposits such as Cadia East and Galore Creek. However, the determination of discrete exploration targets still remains a difficult task for several reasons. The high-grade metal concentrations are typically associated with small volume, pipe-like intrusions that may have aerial extents of only a few hundred square meters (Wilson et 9  al., 2002). Supergene enrichment is poorly developed due to the low pyrite contents of the hypogene alteration assemblages (Cooke et al., 2002) and/or the occurrence of recent glacial erosion as is typical for British Columbia.  Furthermore, the lack of extensive peripheral  hypogene alteration hinders identifying the focus for fluid flow more than several hundred meters away from the mineralized porphyry centre (Deyell et al., 2004). In order to provide more effective exploration tools, it is fundamentally important to address elementary questions concerning the hydrothermal genesis of this particular deposit type. By combining detailed field work with targeted and well constrained geochemical research, it may be possible to recognize subtle or cryptic alteration zones or geochemical dispersion halos highlighting proximity to a mineralized intrusive centre.  1.5 Previous research Because of the remote location of the Galore Creek district, only limited research has been conducted and published prior to this dissertation. The regional and district geology, as well as the exploration context of the Central Zone deposit, have been described by several workers of the operating companies, the Geological Survey of Canada (GSC), the British Columbia Geological Survey (BCGS), and MDRU (Logan et al., 1989a, 1989b; Logan and Koyanagi, 1994; Lueck and Russel, 1994; Lang et al., 1995a, 1995b; Logan, 2005). The geochronology for the Central Zone was first established by Mortensen et al. (1995). The most recent geological synthesis of the Galore Creek district has been published by NovaGold Resources Inc. and MDRU (Schwab et al., 2008). In 1992, MDRU initiated a number of geochemical pilot studies on the Central Zone rocks in order to increase the understanding of the poorly studied alkalic porphyry deposit type. Stanley et al. (1992) conducted a geochemical analysis of major oxides on unaltered samples of 10  intrusive lithologies and determined the metaluminous, alkaline, and silica-undersaturated character of the intrusive suite. In addition, they constrained the magmatic evolution of the intrusive suite and identified a pre- to syn-mineral syenitic and post-mineral monzonitic sublineage. This two-fold classification of the Galore Creek intrusive rocks provides several important insights into the magmatic and hydrothermal evolution (Stanley et al., 1992). Initial sulfur isotope studies on sulfides derived from the Central Zone have shown that δ34Ssulfide values across the whole of the CZ range between –2 and -13‰ (Shannon, 1983; Thompson and Stanley, 1992; Deyell and Tosdal, 2004). In all studies a slight correlation of negative δ34Ssulfide values with increased Au values in the northern and southern portion of the Central Zone were observed, whereas the cupriferous core of the Central Zone did not show any discernable correlation. The studies lacked a sufficient understanding of the intrusive and hydrothermal paragenesis to constrain the samples effectively; nevertheless, they provided essential indicators towards the potential source and geochemical evolution of the hydrothermal fluid system. Calcic alteration is widespread in the Central Zone. The greatest abundance of garnet occurs within the CRZ, and is directly linked with a hydrothermal breccia body. Garnet occurs as a primary cement phase within the hydrothermal breccia. Individual garnet grains display optical zoning with colour and mineralogical variations in growth bands ranging in scale between one and hundreds of microns. Dunne et al. (1995) conducted a petrographic and electron microprobe analysis on few zoned garnet grains and delineated up to five cycles of garnet growth that correlate with variations in several oxides. Based on these observations, Dunne et al. (1995) first suggested that the chemical variations may record the cyclic or pulsating nature of the hydrothermal system. Another study on the Central Zone garnets by Russell et al. (1999) demonstrated the significance of garnets as active tracers for the redox state  11  in the hydrothermal systems. The lack of a robust paragenetic framework made it difficult to constrain the samples effectively.  1.6 Overview of the dissertation This dissertation is presented as four chapters (chapters 2 to 5), each of which represents a manuscript to be submitted to a refereed journal for publication. The focus of each chapter lies on different aspects of the geology and mineralization of the Central Zone deposit. However, some overlap and repetition between the chapters could not be avoided as each contribution has been prepared as a stand-alone publication. Chapter 2 documents the lithological characteristics and stratigraphic evolution of the host-rock units of the Central Zone based on observations from drill core. It further discusses the clastic lithofacies, architecture, and evolution of the Central Zone’s breccia bodies in details, and comments on their role as a precursor for mineralization. Based on detailed descriptions of the host rocks’ coherent or clastic composition, texture, and mineralogy, it was possible to deduce both primary lithological and secondary hydrothermal system-driven processes that led to their deposition. Chapter 3 describes in detail the hydrothermal evolution of the Central Zone deposit based on the lithological architecture, hydrothermal alteration assemblages, and sulfide zonation patterns. This information, together with new U-Pb geochronology constraints on hydrothermal titanite is integrated into an evolutionary ore deposit model for the Central Zone. Chapter 4 describes and discusses the geochemistry and S-isotopic composition of wall rock alteration at the Central Zone deposit. Firstly, the multi-element and isotope analytical methods applied in the characterization of lithological units, hydrothermal alteration assemblages and zones of high-grade mineralization are documented. Secondly, the subtle or cryptic alteration zones or geochemical dispersion halos highlighting proximity to a mineralized 12  intrusive centre at known deposits are described. Finally, the combined techniques and their application to Galore Creek alkalic porphyry deposits are assessed. Chapter 5 documents that by analyzing the major and trace element chemistry of garnet grains with respect to crystal morphology, it is possible to gain insights into hydrothermal processes such as changes in fluid composition, fO2 conditions, and vigour of fluid flow, as well as the scale on which they act. In this study we present petrographic and chemical analyses of 23 individual garnet grains representative of the core of the Central Zone’s calcic alteration footprint.  13  1.7 References Allen, D.G., Panteleyev, A. and Armstrong, A.T., 1976. Porphyry copper deposits of the alkalic suite: Galore Creek, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 402-414. Anderson, R.G., 1984, Late Triassic and Jurassic magmatism along the Stikine Arch and the geology of the Stikine Batholith, north-central British Columbia: Geological Survey of Canada, v.84-1A, p.67-73. Barr, D.A, Fox, P.E., Northcote, K.E. and Preto, V.A., 1976. The alkaline suite porphyry deposits; a summary, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 359-367. Cooke, D.R., Wilson, A.J., Lickfold, V., and Crawford, A.J., 2002, The alkalic Au-Cu porphyry province of NSW: AusIMM 2002 Annual Conference, Auckland New Zealand, pp. 197202. Deyell, C.L., and Tosdal, R.M., 2005, Alkalic Cu-Au deposits of British Columbia: sulfur isotope zonation as a guide to mineral exploration: British Columbia Geological Survey, p. 191-208. Dunne, K.P.E., Lang, J.R., and Thompson, J.F.H., 1994, Fluid inclusion studies of zoned hydrothermal garnet at the Galore Creek Cu-Au porphyry deposit, northwestern British Columbia: Geological Association of Canada-Mineralogical Association of Canada, Program with Abstracts v. 19, p. A31. Enns S.G., Thompson, J.F.H., Stanley, C.R. and Yarrow, E.W., 1995. The Galore Creek porphyry copper-gold deposits, northwestern British Columbia in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordillera of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 640-644. Fields, C.W., Zhang, L., Dilles, J.H., Rye, R.O., and Reed, M.H., 2005, Sulfur and oxygen isotopic record in sulfate and sulfide minerals of early, deep, pre-Main Stage porphyry Cu–Mo and late Main Stage base-metal mineral deposits, Butte district, Montana: Chemical Geology, v. 215, p. 61– 93. Holliday, J.R., Wilson, A.J., Blevin, P.L., Tedder, I.J., Dunham, P.D., and Pfitzner, M., 2002, Porphyry gold-copper mineralisation in the Cadia district, eastern Lachlan Fold Belt, New South Wales, and its relationships to shoshonitic magmatism: Mineralium Deposita, v.37, p.100-116. Jensen, E.P., and Barton, M.D., 2000, Gold deposits related to alkaline magmatism: Reviews in Economic Geology, v. 13, p. 279-314. Lang, J.R., Lueck, B., Mortensen, J.K., Russell, J.K., Stanley, C.R. and Thompson, J.F.H., 1995a, Triassic-Jurassic silica-undersaturated and silica-saturated alkalic intrusions in the 14  Cordillera of British Columbia: Implications for arc magmatism: Geology, v. 23, p. 451454. Lang, J.R., Stanley, C.R., Thompson, J.F.H., and Dunne, K.P.E., 1995b, Na-K-Ca magmatic hydrothermal alteration in alkalic porphyry Copper gold deposits, British Columbia, in Thompson, J.F.H., ed., Magmas, Fluids, and Ore Deposits: Mineralogical Association of Canada, v. 23, p. 339-366. Logan, J.M., 2005, Alkaline magmatism and porphyry Cu-Au deposits at Galore Creek, northwestern British Columbia: B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2004, Paper 2005-1, p. 237-248. Logan, J.M., and Koyanagi, V.M., 1989a, Preliminary Geology and Mineral Deposits of the Galore Creek Area, North-western British Columbia (104G/7W): B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1989-1, p. 269-284. Logan, J.M., and Koyanagi, V.M., and Rhys, D.A., 1989b, Geology and mineral occurrences of the Galore Creek Area (104A and B): B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1989-8. Logan, J.M., and Koyanagi, V.M., 1994, Geology and mineral deposits of the Galore Creek area, northwestern British Columbia (104G/3 and 4): BC Ministry of Energy, Mines, and Petroleum Resources, Bulletin 92, p.96. Lueck, B.A. and Russell, J.K., 1994. Silica-undersaturated, zoned, alkaline intrusions within the British Columbia Cordillera: B.C. Ministry of Energy, Mines and Petroleum Resources, Report: 1994-1, p. 311-315. Monger, J.W.H., 1977. Upper Palaeozoic rocks of the western Canadian Cordillera and their bearing on Cordilleran evolution: Canadian Journal of Earth Sciences, v. 14, p. 18321859. Mortensen, J.K., Ghosh, D. and Ferri, F., 1995. U-Pb age constraints of intrusive rocks associated with copper-gold porphyry deposits in the Canadian Cordillera, in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordillera of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 142-158. Nelson, J., and Mihalynuk, M., 2004. Mega-terranes and deep structures: tectonics and the potential for major new mineral deposits in British Columbia: Mineral Exploration Roundup. Abstract with Programs, p. 26. NovaGold Resources Inc., 2008. NovaGold Expands Galore Creek Resource Estimate. Press release from June 10th, 2008, URL <http://www.novagold.com/upload/pdf/NGReserve ResourceTable.pdf>. Panteleyev, A., 1976., Galore Creek Map Area in Geological Fieldwork 1975, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1976-1, p. 79-81.  15  Russell, J., Dipple, G.M., Lang, J.R. and Lueck, B., 1999. Major-element discrimination of titanium andradite from magmatic and hydrothermal environments; an example from the Canadian Cordillera: European Journal of Mineralogy, v. 11, p. 915-935. Saunders, J.A., 1991, Geology of the Boulder County gold district, Colorado: U.S. Geological Survey Bulletin, 1857-1, p. 137-148. Shannon, S.S. Jr., Finch, R.J., Ikramuddin, M., and Mutschler, F.E., 1983, Possible sedimentary sources of sulfur and copper in alkaline-suite porphyry copper systems: The Geological Society of America, 96th annual meeting, Abstracts with programs, v. 15, no. 6, p. 684. Souther, J.G., 1972, Telegraph Creek Map, British Columbia: Geological Survey of Canada, Paper 71-44, p.38. Schwab, D. L, Petsel, S., Otto, B. R., Morris, S. K., Workman, E. and Tosdal, R. M., 2008, Overview of the Late Triassic Galore Creek Copper-Gold-Silver Porphyry System, in Spencer, J.W., and Titley, S.R., eds., Ores and orogenesis: Circum-Pacific tectonics, geologic evolution and ore deposits: Tucson, Arizona Geological Society Digest 22, p. 471-484. Stanley, C.R., 1992, The Igneous Petrogenesis of the Galore Creek Intrusive Suite. In: Porphyry Copper Gold Systems of British Columbia. Annual Technical Report Year 1, MDRU. Werle, J.L., Ikramuddin, M. and Mutschler, F.E., 1984. Allard Stock, La Plata Mountains, Colorado: An alkaline rock-hosted porphyry copper-precious metal deposit: Canadian Journal of Earth Sciences-Journal Canadien des Sciences de la Terre, v. 21, p. 630-641. Wilson, A.J., Cooke, D.R., Harper, B.J., and Deyell, C.L., 2007, Sulfur isotopic zonation in the Cadia district, NSW: Exploration significance and implication for the genesis of alkalic porphyry gold-copper deposits: Mineralium Deposita, v. 42, no.5, p. 465-487.  16  2  Lithological description and interpretation of the host-rocks of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada1  2.1 Introduction Exploration for (calc-) alkalic porphyry Cu-Au (-Mo) deposits is strongly dependent on a good understanding of the host-rock stratigraphy and the lithological and structural architecture of the prospective district. Detailed descriptions of the host rocks’ coherent or clastic composition, texture and mineralogy are essential in the deduction of primary lithological and secondary hydrothermal system-driven processes. The interplay between these processes and mineralization events is integral to ore deposition. This is particularly true in regards to the formation of breccia complexes in the porphyry environment, where primary permeability and cementation processes directly influence fluid flow and the potential entrapment of sulfides. Alkalic Cu-Au porphyry deposits are known in only a few metallogenic terranes, notably the Triassic and Jurassic marine volcanic arcs of British Columbia (Barr et al., 1976; Lang et al., 1995c) and the Ordovician and early Silurian Lachlan Fold Belt in New South Wales, Australia (Wilson et al., 2003; Cooke et al., 2007). Several of the British Columbian porphyry districts such as Mt. Polley, Afton and Ajax, as well as Copper Canyon and Galore Creek (Fig. 2.1A), are hosted in alkaline (or shoshontic) volcano-sedimentary rocks and syenitic to monzonitic intrusions. They are also characterized by large breccia complexes that host, in some cases, the dominant portion of sulfide mineralization in the system. The Galore Creek district, British  1  A version of this chapter will be submitted for publication. Micko, J., Tosdal, R.M., Chamberlain, C.M, and Simpson, K.A. (2010) Lithological description and interpretation of the host-rocks of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada.  17  Columbia is arguably the most important example of the silica-undersaturated class of alkalic Cu-Au porphyry deposits (Lang et al., 1993). It is located in northwestern British Columbia, about 97 km northeast of Wrangell, Alaska (Fig. 2.1A).  Figure 2.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing location of the Galore Creek Copper porphyry Au-Cu district and other porphyry Cu centers. Red Box outlines the area shown in Fig. 2.1B. B) Regional geology of the northwestern Stikine Terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994).  To date, the combined measured and indicated resources at Galore Creek are estimated at 785.7 million tonnes grading at 0.52% Cu, 0.29g/t Au and 4.87g/t Ag (NovaGold Resources Inc., June 2008). Overall, the district contains five deposits and seven prospects that define a five kilometer long northwesterly trending corridor. The largest of the known prospects is the Central Zone deposit (CZ) combines three mineralized centres called the North Gold Lens (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL; Fig. 2.2). 18  Figure 2.2: Interpreted surface bedrock geology of the Central Zone showing location from three E-oriented crosssections and one N-oriented long section that crosscut the three principal mineralized centers of the North Gold Lens (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL). Also shown is the location of the Bountiful Zone (BZ) that underlies the CZ in the South. Geology modified after NovaGold Resources Inc. (2007).  In this paper, we document the lithological characteristics of the host-rock units of the CZ. The clastic lithofacies, architecture, and evolution of the CZ breccia bodies and their role as a precursor for mineralization are also discussed.  19  2.2 Regional geology The Quesnel and Stikine terranes represent distinct segments of an extensive tectonic collage of allochtonous oceanic and proximal to distal pericratonic terranes collectively termed the Intermontane Belt (Monger and Irvine, 1980; Monger et al., 1982; Coney, 1989). Both the Stikine and Quesnel terranes share a great number of geological characteristics including the presence of alkalic porphyry systems, which has led workers to believe that both terranes are segments of the same Triassic marine arc that experienced oroclinal bending during progressive amalgamation of the marine arcs to North America in the early Jurassic (Wernecki and Klepacki, 1988; Nelson and Mihalynuk, 1993; Mihalynuk et al., 1994; Nelson and Colpron, 2007; Colpron et al., 2007). In combination, both terranes contain the largest concentration of alkalic porphyry Cu-Au deposits and prospects in the world. The deposits and prospects are scattered over the 1500 km strike length of the late Triassic and Early Jurassic magmatic arc that composes the inboard Quesnel and outboard Stikine terranes (Fig. 2.1A). Most silica-undersaturated alkalic porphyry Cu-Au deposits were emplaced in two episodes and are interpreted to have formed outboard of ancestral North America (McMillan, 1991). The first episode took place between 210 and 200 Ma (Mortimer, 1987; Mortensen et al., 1995; Logan et al., 2007), whereas the second, after a hiatus of 10 to 15 million years, corresponds to a major Cordilleran-long shortening and deformation event (Monger et al., 1992; Mortensen et al., 1995) in the early Jurassic (180-190 Ma).  2.3 District geology The Galore Creek district, located at the northwestern margin of the Stikine terrane (Fig. 1A), is hosted within the lower Devonian to upper Permian Stikine assemblage and the lower to upper Triassic Stuhini Group (Figs. 2.1B and 2.3). The oldest rocks of the Stikine assemblage 20  lying northeast of Galore Creek (Fig. 2.1B) are strongly deformed Devonian to Permian limestones, interbedded with mafic and intermediate lavas and volcaniclastic units, as well as a thin succession of middle Triassic siltstones, sandstones, and cherts (Monger, 1977; Enns et al., 1995; Logan, 2005). Unmetamorphosed rocks of the upper Triassic Stuhini group that underly the Galore Creek valley (Fig. 2.2) are subdivided into a lower unit of submarine basaltic to andesitic volcanic rocks interspersed with locally derived sandstones and siltstones (Allen et al., 1976) and an upper unit of partially subaerial, compositionally distinct alkali-enriched volcanic and volcanogenic sedimentary rocks (Fig. 2.2). The Stuhini Group rocks host the Late Triassic alkalic intrusive complex and the related hydrothermal systems. Early main stage hydrothermal activity in the CZ has been dated at 211±1.6 Ma shrimp U/Pb age for hydrothermal titanite (Micko et al., in review; chapter 3).  Figure 2.3: Regional stratigraphy and volcanic to volcaniclastic facies interpretation of the Galore Creek upper Triassic successions in the Central Zone. The blue box indicates the relative lithofacies distribution recognized in the Central Zone. Modified after Logan and Koyanagi (1994).  21  Sedimentary rocks equivalent to the lower Jurassic Hazelton Group that postdate mineralization are preserved north and east of Galore Creek, as are the lower Jurassic to lower Tertiary successor-basin sedimentary rocks of the Bowser Lake and Sustut Groups (Fig. 2.1B; Allen et al., 1976; Logan, 1989a, b; Enns et al., 1995). The upper Cretaceous to Palaeocene Coast plutonic complex occurs as several distinct granitoid phases west of Galore Creek. Steeply inclined (60° to 75º westerly) Eocene quartz monzonite and diorite stocks, as well as mafic to felsic dykes of unknown age, intrude the Triassic rocks throughout the CZ. These young dikes are concentrated in west- and north-striking zones that presumably exploited a pre-existing fault or fracture mesh (Enns et al., 1995). The Galore Creek district is interpreted to have undergone early and broad-scale Triassic north-south compression followed by post-early Jurassic development of northerly trending folds and thrust faults (Logan and Koyanagi, 1994). The CZ lies in the footwall of a west-directed brittle thrust fault (Fig. 2.2) that superposes tightly folded and weakly metamorphosed rocks of the Stuhini Group over petrologically similar rocks in the footwall that host the porphyry Cu-Au systems (Logan 2005; Schwab et al., 2008; Micko et al., in review; chapter 3). District-scale deformation associated with this thrust fault may have been responsible for the observed 45 to 60°W dip of the CZ. Small displacement reverse faults cut the Stuhini Group rocks, the intruding syenite and monzonite intrusions, and the porphyry Cu-Au centers (Fig. 2.2; Schwab et al., 2008; Byrne, 2009).  2.4 Methodology Due to the lack of outcrop in the CZ, the study was reliant on core logging. The CZ contains a vast number of historic drill-holes oriented on an E-W grid. On the basis of this grid three E-W oriented sections were constructed that cross-cut the Au-rich NGL (N 6335547), SGL 22  (N 6334100) and the Cu-dominated CRZ (N 6335100). In addition, one N-S-section (E 351000) was created to link the information gathered from all three mineralized bodies and provide a 3Daspect on the geological framework (Fig. 2.2). Individual drillholes were chosen on the basis of availability of historic core as well as overall spacing relative to neighbouring DDHs on the same section (<100m distance between DDHs). Along these sections a total of 24 diamond drill holes (DDHs) were re-logged that are representative of 12,495 metres of core. The graphic core logging method applied incorporates aspects of the Anaconda mineral mapping technique. This method records relative mineral distributions via the application of colour codes in parallel columns (A1.1). In terms of sulfide distributions relative values were recorded in addition to exact assay data provided by NovaGold Resources Inc. This logging approach facilitates crosscorrelation between geology, textural and structural features as well as alteration assemblages. The dominant logging scale is 1:500 (m), whereas in section of essential detail a 1:100 (m) scale was applied. In addition to the logging efforts, a large number of representative core samples were taken for petrographic investigation. Lithological units are described on the basis of characteristic mineralogy and textures using the terminology and criteria (Table 2.1) outlined by McPhie et al. (1993). The characterization of clastic facies in breccia bodies in respect to the infill type (matrix or cement) are based on criteria (Table 2.1) defined by Davies et al. (2008b). This approach deviates from the exploration-focused rock codes used by Kennecott, NovaGold Resources Inc., and published literature (i.e. Enns et al., 1995); it was chosen in order to better accommodate the CZ’s geological complexity. All rock units are presented in stratigraphic order from oldest to youngest. This stratigraphic sequence was determined on the basis of cross-cutting relationships and forms the foundation for a relative timeline to document the temporal evolution of the Central Zone’s magmatic-hydrothermal system.  23  Table 2.1: Summary of key terminology used in the lithological decrisption of the CZ host-rocks. Based on terminology and criteria defined by MacPhie et al. (1993) and Davies et al. (2008b). Terminology  Definition  Coherent facies  Coherent facies are formed from the cooling and solidification of molten lava or magma and are characterized by porphyritic or aphyric textures.  Clastic facies  Clastic facies in comparison have a fragmental texture and include facies that are interpreted to be derived from sedimentary, volcanic or hydrothermal processes.  Breccia matrix  The matrix is collective term for the fine-grained clastic components of a breccia that occurs between larger clasts. The matrix comprises cominuted wallrock (i.e. lithic and and crystal fragments) of sand to granule size (<0.5-4mm), whereas the finest components are known as rock-flour.  Breccia cement  The cement is the crystalline component within a clastic rock or fracture that precipitated either from an aqueous fluid (commonly sulfides or gangue minerals), or from a magma (i.e syenite-cemented breccia). Cement precipitated from aqueous fluids is a diagnostic component of most hydrothermal breccias.  Juvenile clast  Juvenile clasts are derived by fragmentation of a parental magma that interacted with subsurface or hydrothermal fluids to produce delicate, whispy margins. The preservation potential of whispy clast margins is low when transported, but when found is indicative of magmatic contribution to breccia formation.  2.5 Rock units of the Central Zone 2.5.1  Supracrustal host-rocks  Lower to upper Triassic rocks form the basement to the CZ and host the dominant portion of the sulfide mineralization in the CZ. From oldest to youngest, these rocks are subdivided into one lower to middle Triassic sedimentary unit and four upper Triassic volcanosedimentary formations that collectively represent the Stuhini group at Galore Creek (Souther, 1971; Monger, 1980; Logan and Koyanagi, 1994). The upper Triassic rocks define a volcanic edifice centered on or in the vicinity of Galore Creek (Logan and Koyanagi, 1994) and thus present a variable spectrum of proximal (dominantly coherent) and distal (clastic) lithofacies  24  (Fig. 2.3). All of the encountered strata in the CZ strike west-northwesterly and dip 45° to 60º south-southwest (Fig. 2.2). Fine-grained sandstone to siltstone and ribbon chert were intersected at depth in the NGL (Figs. 2.4A and 2.4B) and form the stratigraphically lowest unit. The rock unit’s clastic matrix is composed of silt, fine sand, and bands of coherent chert. Texturally, it is characterized by planar laminations and/or soft sediment deformation (Figs. 2.4A and 2.4B). The primary composition of the rock unit is obscured by extensive hydrothermal alteration. These sedimentary rocks are assigned to the base of the lower to middle Triassic rocks composed of a submarine unit of silty argilites containing the middle Triassic fossil Daonella cf. Degeeri Boehm, siltstones and ribbon chert (Monger, 1977; Logan and Koyanagi, 1994; Enns et al., 1995).  25  26  Figure 2.4: Lower to upper to Triassic supracrustal host rocks in the Central Zone. A) GC0734 -795.00m, and B) GC0734-811.50m show a siltstone, sandstone and ribbon chert with disseminated bornite (bn), chalcopyrite (cp), orthoclase (or), and biotite (bio) distributed along laminations. An anhydrite (anh) vein crosscuts the assemblage in A. C) GC0734-642.80m and D) GC0702-337.63m presents a hornblende and orthoclase-phyric basaltic andesite. In C) the rock is moderately altered and crosscut by biotite veins. A granitic clast is incorporated in the groundmass and replaced by chlorite (chl), biotite, orthoclase, and pyrite (py). In D) the groundmass and orthoclase-phyric xenolith is replaced by finely, disseminated garnet, biotite, and pyrite. E) GC0702-205.33m and F) GC0573345.63m shows Augite-phyric basalt. In E) the volcaniclastic conglomerate contains an orthoclase and carbonate (car) replaced clasts incorporated in a chlorite, biotite, and garnet replaced clastic matrix. In F) a coherent augitephyric lavaflow is shown. The groundmass is replaced by orthoclase, pyrite, and garnet, whereas the augite phenocrysts are locally affected by biotite and magnetite (mag) alteration. G) GC0573-102.20m and H) GC0448537.50m represent the pseudoleucite (ps)-phyric trachyte and derivative rocks. G) shows a planar laminated, slightly biotite and chalcopyrite replaced pseudoleucite-phyric trachyte derived sand- and siltstone, whereas H) presents A fluidally-shaped pseudeoleucite-phyric peperite intruded into coarse sandstone. I) GC0734-588.80m and J) GC0725-510.20m present the Orthoclase-phyric trachyte. The sample I) is locally replaced by anhydrite and chalcopyrite and incorporates small augite-phyric inclusions. Sample J) is derived from the SGL and represents a coherent unit replaced by biotite, chalcopyrite, and garnet.  27  The sedimentary rocks are conformably overlain by upper Triassic sub-alkaline hornblende and plagioclase-phyric basaltic andesite (Figs. 2.4C and 2.4D) that include both coherent and clastic facies intercepted in the NGL only. In the western and eastern-most portions of the NGL sub-volcanic intrusions or lavas are dominant and characterized by flow-aligned feldspar and hornblende phenocrysts in a groundmass of chlorite and feldspar (Table 2.2). In the eastern portion of the NGL the coherent rocks contain abundant orthoclase-phyric xenoliths that are strongly affected by hydrothermal alteration masking their primary composition. A second population of xenoliths has been recognized in both coherent and clastic facies throughout the NGL. These are composed of coarse interlocking crystals of quartz, feldspar, and altered biotite with a granitic texture. A monomictic volcanic conglomerate is located in the center of the NGL. The fine-grained matrix and clasts derived from the hornblende and plagioclase-phyric basaltic andesite are commonly indistinguishable due to hydrothermal alteration. Only where hydrothermal alteration forms distinct metasomatic rinds on fragments an approximate account of the clast size and abundance can be established (Table 2.2). In these areas, the size and density of clasts varies greatly over a short distance.  28  Table 2.2: Supracrustal hostrocks - lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. Clastic lithologies  NovaGold lithocode  Silt- to sandstone, and/or ribbon chert  n/a  Lithological description Matrix: siltstone to fine grained sandstone (argillite?); bands of siliceous chert; pale pink to green Texture: planar and deformed laminae; thickness: 0.5 to 2cm  Hornblende and plagioclase-phyric basaltic andesite  V4, V5  Sub-volcanic intrusion  Phenocrysts: bimodal: orthoclase and hornblende; size: 0.1 to 0.3cm; abundance: 10 to 15%; euhedral to subhedral; evenly distributed Groundmass: chlorite and plagioclase; aphanitic; medium to dark green Texture: contains rounded, orthoclase-phyric syenite xenoliths (size: 2 to 6 cm; abundance <2%) and granitic xenoliths (size: 1 to 5cm; abundance: <2%)  Volcanic conglomerate  Matrix: fine grained chlorite and plagioclase Clasts: contains hornblende and plagioclase-phyric basaltic andesite clasts (size: 1 to 8cm; abundance: >35 to 50%) and sparse granitic xenoliths (size: 1 to 5cm; abundance: <1%)  Augite-phyric basalt  V1  Sub-volcanic intrusion  Phenocrysts: augite; size: 0.1 to 0.7cm; abundance: 5 to 15%; euhedral to subhedral; evenly distributed Groundmass: biotite, hornblende; aphanitic to finely crystalline; dark green to black Texture: contains lithic and granitic clasts (size: 0.5 to 1.0cm; abundance: <1%)  Volcanic conglomerate  Matrix: Fine grained biotite, hornblende, and broken augite crystal shards Clasts: contains augite-phyric clasts (size: 1 to 6cm; abundance: > 60%) as well as granitic xenoliths and lithic fragments (size: 0.5 to 1cm; abundance: <1%)  Pseudoleucite-phyric trachyte  i1-i2, V2  Sub-volcanic intrusion  Phenocrysts (locally bimodal): (a) pseudoleucite; size: 0.3 to 1.2cm; abundance: 10 to 25%; euhedral to subhedral, trapezohedral, rarely broken; (b) orthoclase; size: 0.1 to 0.3cm; abundance: 5 to 7%; subhedral; tabular Groundmass: hydrothermally altered, may have contained orthoclase, leucite ± various feldspathoids; aphanitic; pale grey to pink Texture: occurs as small intrusion (thickness: 80cm to 1.5m) and intrusive hyaloclastite (peperites) with distinctly fluidal margins (average size: 1 to 35cm)  Fine volcanic silt to sandstone(1) and polymictic pebble conglomerate/ breccia (2)  V2  (1) Fe-rich siltstone to sandstone (argillite?); planar laminae (thickness: 0.5 to 1cm); sparse cm-sized slumpstructures (soft sediment deformations) (2) Polymictic conglomerate/ breccia; subrounded to angular, granules to pebbles (abundance: 85 to 90%) in  29  Clastic lithologies  NovaGold lithocode  Lithological description a fine to coarse sand-sized matrix; individual sequences are up to 35m thick Texture: contains remnant features that remind of marine fossils (i.e. bivalves, brachiopods)  Orthoclase-phyric trachyte Sub-volcanic intrusion or lava flow  V3  Phenocrysts: orthoclase; size: 0.3 to 1.2cm; abundance: 10 to 15%; intact, equant to tabular, euhedral to anhedral, irregularly distributed Groundmass: fine grained orthoclase and biotite; aphanitic; dark grey to black Texture: The NGL unit contains augite-phyric basalt derived clasts ; size : 1 to 15cm ; abundance : <5%; subangular to subrounded  30  Basaltic andesite units are conformably overlain by sub-alkaline to alkaline augite-phyric basaltic rocks that include both coherent and clastic facies. This unit was intercepted in the NGL only (Figs. 2.4E and 2.4F). Coherent units such as lavas and/or sub-volcanic intrusions dominate. They contain abundant augite phenocrysts embedded in a dark green to black, aphanitic to fine crystalline groundmass composed of pyroxene and plagioclase (Figs. 2.4E and 2.4F; Table 2.2). Locally small granitic xenoliths are present. Less abundant monomictic volcaniclastic conglomerate in the east and center of the NGL is characterized by augite-phyric basalt clasts in a fine-grained matrix of very similar composition that contains broken augitephenocrysts. Very rare ‘granitic’ xenoliths and lithic fragments of unknown origin are also present. The augite-phyric basaltic rocks are conformably overlain by pseudoleucite-phyric trachyte and derivative clastic rocks. These are the most abundant rocks in the CZ and an important host for sulfide mineralization. The volcano-sedimentary rocks range from siltstone to sandstone to conglomerate/breccia, and predate the cogenetic coherent rock units. Overall, the volcanogenic sedimentary succession fines from the NGL towards the SGL. Volumetrically important strata of coarser grained conglomerates are composed of polymictic granules to pebbles embedded in a fine to coarse sand-sized matrix (Figs. 2.4G and 2.4H). Hydrothermal alteration obscures the composition and textures of the sedimentary rock, but it is believed to be dominantly argillic with lithic clasts components. The finer clastic facies show planar lamination of Fe-rich siltstone and sandstone. Rarely, cm-sized slump-structures are preserved that indicate a fining upwards orientation. Sub-volcanic intrusions occur throughout the CZ and crosscut the volcanogenic units including the cogenetic volcano-sedimentary rocks. They form small intrusions that contain abundant pseudoleucite phenocrysts and sparse orthoclase phenocrysts. These rocks are commonly affected by hydrothermal alteration. However, the primary igneous  31  mineral assemblage likely was composed of orthoclase, leucite, and various feldspathoids. Domains of pseudoleucite-phyric clasts are locally associated with coherent intrusive bodies. These delicate clasts with fluidal margins locally cross-cut laminations and are interpreted to be derived from quench fragmentation by emplacement in wet sediment (i.e. peperites; Fig. 2.4H). Orthoclase-phyric trachyte in the NGL and SGL form volcanic intrusions and/or lava flows composed of abundant flow-oriented, tabular orthoclase phenocrysts embedded in a grey, fine grained to aphanitic orthoclase dominated groundmass (Figs. 2.4I and 2.4J; Table 2.2). The depositional timing of the unit is controversial due to conflicting textural observations in the NGL and SGL. Logan and Koyanagi (1994) describe a thinly bedded unit of tuff, breccia, and rare flows that lie above the augite-phyric basalt in the CZ and contain orthoclase rather than pyroxene crystals. This description correlates well with our observations in the NGL, where the orthoclase-phyric trachyte overlies the augite-phyric basalt. Here, the upper contact of the trachyte unit is sharp, whereas the lower contact is characterized by few clastic inclusions derived from the underlying basalt. This implies an origin of the rock as lava flow that formed prior to the deposition of the pseudoleucite-phyric trachyte derived rocks. In the SGL, however, the intrusion-like, fingering geometry and sharp contact relationship of the orthoclase-phyric trachyte with the pseudoleucite-phyric trachyte derived rocks implies an origin as sub-volcanic intrusion (McPhie et al., 1993), and defines the rock unit as youngest of the Stuhini group. This observation correlates well with descriptions from Enns et al. (1995) and Schwab et al. (2008). It is possible that the orthoclase-phyric trachyte in the NGL represents a sub-volcanic intrusion that exploited the contact between the pseudoleucite-phyric trachyte and the augite-phyric basalt and is synchronous with the intrusion in the SGL. However, despite the great compositional similarity of the rocks units, that they may be of separate origin and timing.  32  2.5.2  The Central Zone intrusive complex (CZIC)  The Central Zone intrusive complex (CZIC) consists of compositionally variable intrusive units that are associated with the development of the hydrothermal system in the CZ, as well as a number of satellite deposits throughout the Galore Creek district. In the CZ, the typically tabular intrusions dominantly strike north-northwest and dip 45° to 60º west-southwest. The CZIC represents an amalgamation of sheet dykes that are believed to be of co-magmatic origin with the alkaline pseudoleucite and orthoclase-phyric trachytes present at Galore Creek and Copper Canyon (Panteleyev, 1976; Enns et al., 1995). The alkaline suite is composed of four principal intrusion types that are distinguished on the basis of varying petrology and crosscutting relationships. Each type has several textural varieties characterized by minor mineralogical variations, such as phenocryst size and abundance. All units of the CZIC contain small, scarce lithic and granitic xenoliths that are described in the supracrustal host rock section above. Orthoclase and pseudoleucite-phyric syenites are common throughout the NGL, but are most frequently intercepted in the form of large clasts within the hydrothermal breccia body of the CRZ. Intrusions are characterized by a bimodal phenocryst population of orthoclase and pseudoleucite embedded in a light to dark grey coloured, “salt and pepper” textured groundmass that consists of fine grained orthoclase and biotite (Fig. 2.5A; Table 2.3).  33  Figure 2.5: Upper Triassic Central Zone intrusive complex. A) GC0492-448.50m shows an orthoclase and pseudoleucite-phyric syenite. B) GC0441-370.94m is an orthoclase-phyric syenite, sub-unit (1) that contains large pseudoleucite-xenocrysts. C) GC0441-370.40m represents the same sub-unit as B), but contains abundant, mmsized pseudoleucite-phenocrysts. D) GC0441-319.13m refers to orthoclase-phyric syenite sub-unit (3). E) GC073250.00m is a megacrystic orthoclase and plagioclase (plag)-phyric monzonite, subunit (1), whereas F) GC0617247.80m refers to sub-unit (3). G) GC0441-218.60m presents an orthoclase-phyric monzonite, sub-unit (1). H) GC0637-149.10m shows the same sub-unit, cementing orthoclase-phryic syenite clasts. This unit can also be referred to as monomictic orthoclase-phyric monzonite-cemented breccia.  34  Table 2.3: Galore Creek intrusive complex – lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. Clastic lithologies  NovaGold lithocode  Orthoclase and pseudoleucite-phyric syenite  i3, i4b  Lithological description Phenocrysts bimodal: (a) orthoclase; size: 0.5 to 1.2cm; abundance: 2 to 3%; subhedral; equant to tabular; (b) pseudoleucite; size: 0.7 to 1.0cm; 1 to 2%; subhedral; trapezohedral Groundmass: orthoclase (70%) and biotite (30%); fine grained; Texture: “salt and pepper” appearance of the groundmass  Orthoclase-phyric syenite  i4a  (textural varieties 1, 2 and 3)  (1) Phenocrysts: orthoclase; size: 0.8 to 1.8cm; abundance: 10 to 15%; euhedral; equant to tabular; flow aligned; sparse pseudoleucite xenocrysts (2.5 to 4cm) and locally small pseudoleucite phenocrysts (0.1 to 0.3cm) (2) Phenocrysts: orthoclase; size: 0.8 to 1.8cm; abundance: 10 to 15%; euhedral; tabular; flow aligned (3) Phenocrysts: orthoclase; size: 0.8 to 2cm, occasionally up to 3cm; abundance: 3 to 5%; euhedral to subhedral; tabular to equant; easily confused with orthoclase-phyric monzonite sub-unit (2) Groundmass: orthoclase (70%) and biotite (30%); fine grained; Texture: “salt and pepper” appearance of the groundmass  Megacrystic orthoclase and plagioclase-phyric monzonite  i5, i9a,b  (sub-units 1, 2 and 3)  (1) Phenocrysts bimodal: (a) orthoclase megacrysts; size: 1.2 to 2.5cm; 3 to 5%; euhedral; equant to tabular; commonly irregularly distributed, locally flow aligned; (b) plagioclase; size: 0.1 to 0.5cm; abundance: 5 to 7%; subhedral; rounded; regularly distributed (2) Phenocrysts bimodal: (a) orthoclase megacrysts; size: 1.5 to 4.5cm; abundance: 5 to 7%; euhedral; tabular; flow aligned; oscillatory zoned; (b) plagioclase; size: 0.1 to 0.5cm; abundance: 5-15%; subhedral; rounded, locally tabular (3) Phenocrysts bimodal: (a) orthoclase megacrysts; size: 1.2 to 3.0cm; abundance: 7 to 10%; euhedral; tabular, flow aligned; (b) plagioclase; size: 0.1 to 0.5cm; abundance: 15 to 35%; subhedral; rounded, locally tabular Groundmass: feldspar (60%), biotite (20%), hornblende (15%), and magnetite (5); coarse grained; light grey to green  Orthoclase-phyric monzonite (sub-units 1and 2)  i6-i10, i11  (1) Phenocrysts: orthoclase; size: 0.5 to 0.8cm; abundance: 1 to 2%; euhedral; equant, locally broken (2) Phenocrysts: orthoclase; size: 0.4 to 1.2cm; abundance: 3 to 5%; euhedral; equant to tabular, locally acicular; flow aligned Groundmass: orthoclase and plagioclase (60%), biotite (35%), and magnetite (5%); medium grained; light grey  35  Clastic lithologies  NovaGold lithocode  Lithological description to green  Monomictic orthoclase -phyric monzonite-cemented breccia (SGL)  B3a  Clasts: orthoclase-phyric syenite; size: 1 to 6 cm; abundance: 5 to 7%; sub-angular to angular; strongly altered Cement: see groundmass above Texture: flow alignment of orthoclase phenocrysts around clasts  Plagioclase-phyric monzodiorite  i10 or D2  Phenocrysts: plagioclase; size: 0.3 to 1cm; abundance: 10 to 15 %; equant; euhedral to subhedral; irregularly distributed Groundmass: plagioclase (50%), hornblende (25%) and biotite (25%); medium grained; equigranular; light grey to green  Aphyric mafic diorite  D1  Groundmass: Biotite and hornblende; aphanitic; dark green to black Texture: Locally hornfelsed at intrusive margins; locally contains rounded, calcite-filled varioles  Aphyric felsic syenite  D3  Groundmass: orthoclase and quartz; aphanitic; beige to light grey  36  Orthoclase-phyric syenites are common throughout the CZ. Their groundmass is dominated by fine grained orthoclase and small amounts of biotite. They commonly contain moderately abundant orthoclase phenocrysts that range in size between 0.8 and 2cm, are equant to tabular in shape and flow-aligned. The intrusion also contains scarce pseudoleucite xenocrysts (Fig. 2.5B). In few core samples small amalgamations of strongly altered, 0.2 to 0.5cm sized pseudoleucite crystals have been recognized that may represent phenocrysts (Fig. 2.5C) rather than xenocrysts (Fig. 2.5B). The class of orthoclase-phyric syenites shows slight variations in porphyritic crystal textures and/or xenocryst abundances throughout the CZ (Table 2.3). Fringing the CZ on the west and forming the host rock to the Southwest zone (Byrne, 2009; Byrne et al., 2010) is a large, composite megacrystic orthoclase and plagioclase phyric monzonite stock (Figs. 2.5E and 2.5F). The unit’s groundmass is light grey to green, coarse grained, composed of orthoclase, plagioclase, biotite, hornblende, magnetite, chlorite, and apatite. The rock commonly has a bimodal phenocryst assemblage that consists of moderately abundant 1.2 to 2.5cm sized tabular and commonly oscillatory zones orthoclase megacrysts as well as 0.2 to 0.4cm, subhedral plagioclase phenocrysts; plagioclase abundances vary between 5 and 15%, in some areas even reach 35% (Fig. 2.5F). Similar to the older class of orthoclasephyric syenite class megacrystic orthoclase-and plagioclase-phyric monzonites also show variations in porphyritic crystal textures and abundances throughout the CZ (Table 2.3). Orthoclase-phyric monzonites are the youngest intrusive units, and are localized in the SGL, where they crosscut megacrystic orthoclase and plagioclase-phyric monzonite. The groundmass is medium grained, composed of primary igneous orthoclase, plagioclase, biotite, hornblende, magnetite, chlorite, and apatite, and thus, very similar to the composition of megacrystic orthoclase- and plagioclase-phyric monzonite. The orthoclase-phyric monozonite commonly contains sparse to moderately abundant, 0.5 to 0.8cm sized, acicular orthoclase  37  crystals that are commonly flow aligned (Fig. 2.5G). However, variations in phenocryst abundance have been recognized throughout the CZ as well. In the center of the SGL the rock unit was found to contain clasts derived from the nearby orthoclase-phyric syenite sheet dyke complex. The sub-angular to angular clasts are 1 to 6 cm in size and moderately abundant over a short distance (< 5m). The lateral extent of this clast-rich unit is unknown and could potentially be classified as a monomictic orthoclase-phyric monzonite cemented breccia (Fig. 2.5H). Several Eocene intrusive units crosscut the CZ. They are easily distinguished by sharp, locally chilled margins. A plagioclase-phyric monzonite to monzodiorite is the earliest of the late intrusions. It contains abundant, 0.2 to 0.3cm sized, subhedral plagioclase phenocrysts embedded in a dark grey to light green, aphanitic, groundmass dominantly composed of plagioclase, hornblende, and biotite. The rock unit is cross-cut by an aphyric mafic diorite that is characterized by a dark green to black, aphanitic groundmass dominantly composed of biotite and hornblende. In some cases the diorite shows hornfels development at intrusive margins; here, calcite-filled varioles are locally visible. The youngest intrusive unit is an aphyric felsic monzonite common throughout the Galore Creek valley and Copper Canyon. Its groundmass is beige to light grey, aphanitic, and dominantly composed of quartz and orthoclase. 2.5.3  Breccia complexes  Breccias complexes are common throughout the CZ. In general, individual breccia bodies have an inclined pipe-like geometry, consisting of variable proportions of clast, matrix, or cement. The volumetrically smallest (100m by 100m; Fig. 2.6) is located in the center of the SGL and is a polymictic matrix breccia (Table 2.4). The sub-angular to sub-rounded clasts are composed of pseudoleucite-phyric trachyte derived sedimentary rocks (60%) and range in size between 0.5 and 12cm (Fig. 2.6). Additional juvenile clasts derived from the orthoclase and pseudoleucite-phyric syenite are fluidally-shaped, and range in size between 1 and 15cm (Fig. 38  2.7A). The fragments form a clast-supported breccia system is infilled with sand- and granulesized matrix of the same material (Figs. 2.6A and 2.6B). Locally, individual orthoclase crystals have been observed that form part of the matrix and are considered a juvenile component (Davies et al., 2008b). A fine crystalline biotite and orthoclase alteration locally replaces the matrix, clast margins, and fills micro-cavities and fractures. The clast/cement ratio is >20:1. The overall morphology and orientation of the breccia is unknown.  39  Figure 2.6: Distribution of rocks in the South Gold Lens (section 6334100). The matrix bearing breccia body contains rocks A) and B). A) GC0448-275.00m shows a fluidal, juvenile orthoclase-phyric syenite derived clast embedded in a coarse sandstone matrix, whereas B) presents a laminated sand- to siltstone clast incorporated into a sandstone to pebble-stone matrix. The cement-bearing breccia contains rocks C) and D). C) GC0637-158.50m is composed of jigsaw fit orthoclase-phyric monzonite derived clasts cemented by dentritic diopisde and anhydrite. The diopside is locally replaced by epidote (epi). D) presents the same clast type cemented by coarse biotite, magnetite, and anhydrite.  40  Table 2.4: Breccia systems - lithological descriptions. NovaGold litho-code descriptions see Enns et al., 1995. Clastic lithologies  NovaGold lithocode  Lithofacies  Polymictic matrix breccia (SGL)  B  n/a  Lithological description Clasts: pseudoleucite-phyric trachyte and derivative rocks (60%); juvenile clast: orthoclase and pseudoleucite-phyric syenite porphyry (40%); size: 0.5 to 12cm (max. 80cm); sub-angular to subrounded, poorly to moderately well sorted Matrix: fine to coarse sand- and granules-sized fragments derived from rock types described above; contains juvenile orthoclase crystals Cement: fine crystalline aggregates of biotite (80%) and orthoclase (20%) Texture: clast/matrix ratio: ~ 4:1; clast/cement ratio >20:1  Polymictic, garnet, biotite, and anhydrite-cemented breccia (CRZ)  B2b  CRZ (1)  Clasts: pseudoleucite-phyric trachyte and derivative rocks (90%), orthoclase and pseudoleucite-phyric syenite (10%); size: 80cm to 2.5m; angular to subangular; jigsaw-fit or slightly rotated; well sorted Cement: fine crystalline aggregates of biotite (35%), oscillatory zoned garnet (20%), magnetite (15%), anhydrite (10%), pyroxene (5%), orthoclase (5%), chalcopyrite and minor bornite (5%); sulfides replace biotite and magnetite in a disseminated manner Texture: dominated by a crackle-fractures and veins, 2 to 10cm thick cemented/filled with the hydrothermal assemblage; clasts become gradually smaller, subangular, and rotated distal to the breccia margin; across the same distance (… m) the clast/cement ratio rapidly changes from ~20:1 to ~4:1  CRZ (2)  Clasts: pseudoleucite-phyric trachyte and derivative rocks (80%), orthoclase and pseudoleucite-phyric syenite (20%); size: 1 to 15cm, closer to the margin up to 80cm; angular to subrounded – clast margins commonly obscured by hydrothermal alteration rinds/cement; rotated; moderately well to well sorted Cement: fine crystalline aggregates and coarse crystals (0.5 to 3cm) of garnet (55%), anhydrite (20%), biotite (10%), pyroxene (5%), magnetite (5%), chalcopyrite and pyrite (5%) infill void spaces with anhydrite and replace biotite and magnetite in a disseminated manner Texture: dominated by large vugs lined by dendritic garnet and biotite infilled with anhydrite and sulfides; locally well sorted, orthoclase and pseudoleucite-phyric syenite dominated clastic domains are recognized; clast/cement ratio: ~ 1:1  41  Clastic lithologies  NovaGold lithocode  Lithofacies CRZ (3)  Lithological description Clasts: pseudoleucite-phyric trachyte and derivative rocks (70%), orthoclase and pseudoleucite-phyric syenite (25%), size: 1 to 15cm, angular to subangular - clast margins locally obscured by hydrothermal alteration rinds/cement, rotated, poorly sorted; juvenile clasts (5%), size: 2 to 25cm, unknown origin; fluidally-shaped; subhedral, equant to tabular orthoclase phenocrysts embedded in an aphanitic, black matrix (volcanic glass?); composition reminds of orthoclase-phyric syenite (see tab. 3) Cement: fine crystalline aggregates and moderately coarse crystals (0.5 to 1.5cm) of garnet (35%), diopside (25%), magnetite (10%), biotite (10%), anhydrite (10%), , chalcopyrite and minor pyrite (5%); sulfides infill void spaces with anhydrite and replace biotite and magnetite in a disseminated manner Texture: Generally comparable with the center lithofacies with the exception of juvenile clasts; locally juvenile clasts mantle fragments and act as magmatic cement; no clastic domains based of rock type or size can be defined; clast/cement ratio: ~ 1:1  Polymictic, diopside, biotite, and magnetite-cemented breccia (NGL)  B2b  NGL (1)  Clasts: pseudoleucite-phyric trachyte and derivative rocks (70%), orthoclase and pseudoleucite-phyric syenite (30%); size: 80cm to 3m; angular to subangular; jigsaw-fit or slightly rotated; well sorted Cement: fine crystalline aggregates and coarse crystals (0.5 to 2 cm) of pyroxene (30%), biotite (20%), magnetite (15%), garnet (10%), orthoclase (10%), and anhydrite (10%); chalcopyrite and minor bornite (5%) replace biotite and magnetite in a disseminated manner Texture: dominated by a crackle-fractures and veins, 2 to 20cm thick cemented/filled with the hydrothermal assemblage; clasts become gradually smaller, subangular, and rotated distal to the breccia margin; the clast/cement ratio rapidly changes from ~20:1 to ~2:1  NGL (2)  Clasts: pseudoleucite-phyric trachyte and derivative rocks (55%), augite-phyric basalt (35%), orthoclase and pseudoleucite-phyric syenite (15%); 1 to 15cm, locally up to 80cm; clast margins strongly obscured by hydrothermal alteration rinds/cement; rotated; moderately well sorted Cement: 5 to 50%; fine crystalline aggregates of pyroxene (30%), biotite (20%), magnetite (15%), garnet (10%), orthoclase (10%), and anhydrite (10%); chalcopyrite, pyrite, and minor bornite (5%) replace biotite and magnetite in a disseminated fashion Texture: dominated by hydrothermal cement assemblage that locally overprints all clastic textures; clast/cement ratio: ~ 1:2  Monomictic magnetite, biotite and diopside-cemented breccia (SGL)  B2b  n/a  Clasts: 2 to 25cm, locally up to 85cm; orthoclase-phyric monzonite (60%), megacrystic orthoclase and plagioclase-phyric monzonite (40%); angular, jigsaw-fit, very little rotation  42  Clastic lithologies  NovaGold lithocode  Lithofacies  Lithological description Cement: fine crystalline aggregates and coarse crystals of biotite (35%), magnetite (25%), pyroxene (20%), anhydrite (15%), and garnet (3%). Bornite and chalcopyrite (2%) infill void spaces and replace biotite and magnetite Texture: dominated by dentritic style cement and anhydride or magnetite filled vugs; clast/cement ratio: ~ 5:1  43  The CRZ is dominated by a polymictic, garnet-biotite-anhydrite cemented breccia that is centered in the CRZ, but extends laterally to the NGL and possibly to the southerly located Bountiful Zone (Fig. 2.2; not part of this study). On the CRZ cross-section (Fig. 2.7), the breccia body extends from the central to western portion of the cross-section and is approximately 650m wide and 850m long. The central wallrock contact in its present geometry trends broadly north and dips 60° to the west. The base and western wallrock contact of the breccia body has not yet been defined by drilling. The CRZ breccia body is internally zoned and can be sub-divided into three principal clastic lithofacies (Fig. 2.7) characterized by differences in clast type, clast size, and overall clast/cement ratio (Table 2.4). The CRZ (1) lithofacies include wallrock contact and about 50 to 100m of the directly adjacent breccia margin. The central wallrock contact is characterized by hydrothermally cemented crackle-breccia stockwork and veins. Adjacent to the contact are distinct angular to subangular clasts that range in size between 80cm and 2.5m. These are jigsaw-fit to slightly rotated, which implies minimal amount of transport. Fragments are derived from the pseudoleucite-phryic trachyte derived sedimentary rocks, and orthoclase and pseudoleucite-phyric syenite (Fig. 2.7A). The CRZ (2) lithofacies are widespread, extending for about 450m to the deep western portion of the CRZ (Fig. 2.8). It contains the same clast types as defined for the CRZ (1) lithofacies. However, individual fragments are distinctly smaller (1 to 15cm), subangular to subrounded, and clast margins are commonly obscured by hydrothermal alteration rinds/cement (Figs. 2.7B and 2.7C). Fragments are rotated and moderately to well sorted. Locally small domains of orthoclase and pseudoleucite-phyric syenite derived clastic domains are mapped. Overall, these characteristics indicate only small to moderate amounts of transport. The CRZ (3) in the deep western portion of the CRZ is characterized by the same clast types described above. However, fragments are angular to sub-angular, 1 to 15cm in size, rotated and poorly sorted indicating minimal to moderate transport and abrasion. In addition, sparse  44  juvenile clasts have been recognized. These are fluidally-shaped, range in size between 2 and 25cm, and contain subhedral, equant to tabular orthoclase phenocrysts embedded in an aphanitic, black aphanitic matrix (Figs. 2.7E and 2.7F). Overall the igneous clasts resemble orthoclasephyric syenite, but cannot be traced to a district intrusion. Throughout the CRZ breccia, two distinct hydrothermal cement domains have been recognized. The crackle-fractured wallrock and breccia margin are dominated by fine crystalline aggregates of biotite, garnet, magnetite, anhydrite, pyroxene, and orthoclase (Table 2.4) that infill fractures, veins and small cavities. Disseminated chalcopyrite, pyrite, and minor bornite commonly replace biotite and magnetite. The clast/cement ratio in the CRZ (1) lithofacies change rapidly from ~20:1 in the crackle-fractured wallrock to ~4:1 in the fragmental margin (Fig. 2.7A). The CRZ (2) and CRZ (3) lithofacies contain fine crystalline aggregates and coarse crystals of oscillatory zoned garnet, biotite, zoned pyroxene, and magnetite that form dendritic cement and distinct alteration rinds on clasts (Figs. 2.7B, 2.7C, and 2.7D). Large anhydrite, chalcopyrite and pyrite crystals infill remnant void spaces, and replace biotite and magnetite. The clast/cement ratio is 1:1. The only difference between the two lithofacies is the presence of juvenile clasts in the CRZ (3). The internal characteristics and geometry of the CRZ breccia body define a moderate westerly to northwestern sub-parallel to the orientation of the CZIC.  45  46  Figure 2.7: Distribution of rocks in the Central Replacement Zone (section 6335100). The cement-bearing breccia body is composed of 3 lithofacies. Litho-facies 1 CRZ 1 contains rocks A) GC0488-197.80m that shows a distinct crackle-fracture framework and void spaces. Diopside and garnet form alteration rinds to the fragments, whereas biotite forms the cement. Litho-facies CRZ 2 contains rocks B, C, and D. B) GC0732-258.00m shows angular orthoclase- and pseudoleucite-phyric clasts with a strong light brown garnet alteration rind, cemented by dark brown garnet and pyrite. C) GC0568-417.00m is a sample strongly dominated by a garnet, biotite, anhydrite, and chalcopyrite cement. D) GC0732-347.00m presents a void space lined by dentritic garnet and filled with anhydrite, chalcopyrite and pyrite. Lithofacies CRZ 3 contains rock samples E) GC0738-523.52m and F) GC0738-534.00m that are characterized by fluidal, juvenile clasts and angular, orthoclase and pseudoleucite-phyric clasts cemented by an assemblage of garnet, biotite, diopside, and magnetite.  47  On the NGL cross-section, the breccia body is located in the west and is approximately 150 to 200m wide and 300 to 350m long. The overall geometry of the breccia is difficult to define as the shallow portion is cut by the younger megacrystic orthoclase and plagioclasephryic monzonite. Nevertheless, two distinct clastic lithofacies have been identified (Fig. 2.8). The NGL (1) lithofacies is formed by the crackle-fractured margin and adjacent breccia margin (Fig. 2.8A) that consist of angular to subangular clasts that range in size between 80cm and 3m. These are jigsaw-fit to slightly rotated and well sorted, which implies minimal amount of transport. Fragments are derived from the pseudoleucite-phryic trachyte and derivative rocks and orthoclase and pseudoleucite-phyric syenite (Fig. 2.8B). The NGL (2) lithofacies compose the dominant portion of the breccia body and extends to the lower wallrock contact. It contains the same clast types as defined above as well as augite-phyric basalt derived clasts. Fragments are small (1 to 15cm, up to 80cm) and texturally obscured by intense hydrothermal cement (Figs. 2.8C and 2.8D). The cement assemblage in the NGL (1) and NGL (2) lithofacies are dominated by fine crystalline aggregates of pyroxene, biotite, magnetite, garnet, orthoclase, and anhydrite (Figs. 2.8B and 2.8C). In some larger fractures and veins large diopsidic pyroxene crystals have been observed (Fig. 2.8A). Disseminated chalcopyrite, pyrite and minor bornite replace biotite and magnetite. Within the veins small aggregates of sulfides occur in association with anhydrite. The clast/cement ratio from the margin to the center of the breccia body changes dramatically from ~20:1 to 4:1 to 1:2 (Fig. 2.8D). The similarity in texture, clast and cement composition between the NGL and CRZ breccia bodies as well as the projected morphology of the CRZ (Fig. 2.7), implies a genetic link between the breccia bodies, as well as a similar internal geometry.  48  Figure 2.8: Distribution of rocks in the North Gold Lens (section 6335547). The cement-bearing breccia body is composed of 2 lithofacies. Litho-facies NGL 1 contains rocks A) and B). A) GC0734-415.25m shows a garnet, diopside, chalcopyrite, bornite, and anhydrite cemented vein cross-cutting the coherent margin of the breccia body, whereas B) GC0501-297.00m presents a biotite and chalcopyrite cemented fractures. Litho-facies NGL=2 contains rocks C) and D). C) GC0501-318.55m shows a biotite, garnet, and chalcopyrite-replaced augite-phyric clast cemented by biotite. D) GC0501-377.60m presents a breccia sample that contains >80% hydrothermal cement (biotite, magnetite, diopside, and garnet). Only locally small clasts are visible largely replaced by garnet and magnetite.  49  The youngest of the hydrothermal breccia bodies is a polymictic, magnetite, biotite, and diopside-cemented breccia body located in the western portion of the SGL. The overall breccia morphology is unknown, as the western extent is not defined by drilling and the eastern extension is limited by a steeply westerly dipping fault. There is no discernable zonation within the breccia; however, the characteristics are similar to a hydrothermal breccia described in the Southwest Zone by Byrne, (2009). The clasts are derived from megacrystic orthoclase and plagioclase-phyric monzonite and the orthoclase-phyric monzonite. The fragments range in size from 2 to 25cm and are angular and commonly jigsaw fit, implying in situ brecciation or a small amount of transport only (Figs. 2.6C and 2.6D). The cement assemblage consists of coarse crystalline aggregates of biotite, magnetite, zoned diopside, and garnet that form dendritic cement (Fig. 2.6C) and alteration rinds around clasts (Fig. 2.6D). The void spaces are infilled with anhydrite and accumulations of intergrown bornite and chalcopyrite. Locally, the sulfides also replace biotite and magnetite in a disseminated fashion.  2.6 Breccia development in the Central Zone 2.6.1  Matrix bearing breccia  The geometry of the SGL matrix-bearing breccia is unclear, as the rock unit is truncated by intrusions. Clasts are subangular to subrounded, poorly to moderately sorted, and embedded in a coarse sand- to granule-sized rock flour matrix that contains juvenile orthoclase crystals. Juvenile clasts with delicate fluidal margins derived from orthoclase-phyric syenite porphyry are ubiquitous in the breccia body, but cannot be linked to an intrusion. This may imply vertical displacement and disaggregation from the parental magma by explosive fragmentation. Microfractures and cavities are cemented by a fine crystalline potassic but sulfide-poor mineral  50  assemblage which indicates the introduction of hydrothermal fluids synchronous or postfragmentation. Overall, the clast distribution and potential vertical displacement, as well as fragment rounding, mixing, and matrix generation, suggests fluidization as a transport mechanism during the sub-surface breccia formation (McCallum, 1985; Sillitoe, 1985; Byrne et al., 2010). 2.6.2  Cement-bearing breccias  The geometry of the SGL breccia body is poorly constrained. In contrast, the distribution of the lithofacies in the CRZ indicates a pipe-like body with an inclination of ~60°W. The maximum inclination for breccia bodies in the porphyry environment has been reported to rarely deviate from vertical orientation by more than 15° (Sillitoe, 1985). Thus, post-depositional tilting of the CRZ breccia system is implied. The NGL breccia may represent an irregular embayment or offshoot from the main CRZ breccia, on the basis of lithological similarities. The clastic lithofacies in the CRZ breccia body show a range from angular to subangular and poorly sorted clasts at depth (CRZ 3) to subangular to subrounded and moderately well sorted clasts in the center (CRZ 2) and adjacent to the fractured margin (CRZ 1) of the breccia. This implies an increase of transport and abrasion towards the center caused by fluidization. Juvenile clasts with delicate fluidal margins present at depth only are likely derived from orthoclase-phyric syenite porphyry and imply explosive fragmentation. In contrast, the SGL cement-bearing breccia body is marked by homogeneous lithofacies that contain angular to subangular, dominantly jigsaw fit clasts indicative of little to no transport or rotation. This may imply that fragmentation was non-explosive. Thus, multiple mechanism for brecciation need to be considered. All breccias bodies are dominated by potassic and calc-potassic mineral assemblages indicative of moderately high temperature hydrothermal fluids of a dominantly magmatic source 51  (Ulrich et al., 2001; Seedorf et al., 2005). The alteration and formation of replacement rinds along clasts implies that hydrothermal fluid introduction took place synchronously with or immediately after brecciation. Clast alteration in the remaining breccia bodies was followed by an episode of open-space fill. First silicate gangue minerals such as garnet and diopside form dendritic cement and later sulfides infilled remnant cavities commonly together with anhydrite (Fig. 2.7D). The cement minerals are coarsely crystallized and oscillatory zoned. Zoning is particularly well developed in garnet. Instead of being homogeneously mineralized, the breccias of the NGL and CRZ contain restricted volumes of ore-grade material along part of the pipe margin. Enhanced permeability resulting from more original open space between fragments and proximity to the apex is believed to account for higher grade mineralization in the marginal parts of the pipe (Sillitoe, 1985). However, geochemical gradients based on contrasting mineralogy between hydrothermal cement and wallrock may also contribute to high Cu-Au grades. 2.6.3  Mechanisms for brecciation in the CZ  Based on the textural and mineralogical characteristics of all breccias, they are interpreted to result from rapid exsolution of an aqueous fluid phase from a hydrous magma followed by decompression of both the exsolved low-density aqueous fluid and the water saturated residual melt (Burnham, 1985). In this case, the hydrous magma is likely an orthoclase-phyric syenite, which in case of the SGL matrix breccia and the CRZ hydrothermal breccia led to the incorporation of juvenile clasts and matrix components (Sheridan and Woheltz, 1981; Hedenquist and Henley, 1985; Byrne et al., 2010). Another potential mechanism is subsurface phreatomagmatic brecciation that is triggered by the interaction between the intruding magma and wet, unconsolidated, or poorly consolidated sediments (steam expansion fragmentation). Phreatomagmatic brecciation may result in a purely explosive fragmentation, non-explosive quench fragmentation, or a combination of both (Davies et al., 2008b). 52  2.7 Conclusions Detailed drill core logging and the petrographic analysis of samples on three E-W crosssections has characterized the lithological units and their paragenesis in the CZ. Lower to upper Triassic sedimentary and volcano-sedimentary rocks form the supracrustal hostrocks to the Central Zone intrusive complex that is directly related to mineralization and brecciation in the system. One matrix-bearing breccia and three cement-bearing breccias have been recognized throughout the CZ. Despite the differences in timing, clastic lithofacies, type of infill (i.e. matrix or cement) all breccia systems are believed to have formed as intrusion-related breccias as defined by Sillitoe, 1985. In addition, a minor phreatomagmatic component to breccia formation is possible. Most porphyry systems along the Pacific rim contain one or more varieties of breccia bodies (Sillitoe, 1985). In many of these systems breccia complexes can be spatially associated with higher grade of Cu-Au mineralization (Seedorff et al., 2005). Here, the increase in permeability provides available space and potential traps for sulfide mineralization commonly introduced by synchronous or post-brecciation hydrothermal fluid influx. Thus, the identification of breccia complexes, and an in depth knowledge of their geometry, lithofacial architecture, and ultimately the evolutionary processes that led to their emplacement, is essential to mineral exploration in the porphyry environment. The CRZ and NGL breccias are directly affiliated with Cu-dominated mineralization. In both systems, the detailed description of the individual lithofacies revealed that ore-grade material is restricted along part of the breccia pipe margin. In addition, the distribution of clastic facies defined a distinct post-brecciation and, thus, a postmineral tilt of the system of ~45 to 60°W. These aspects are essential for the definition of resource location and future mining.  53  2.8 References Allen, D.G., Panteleyev, A. and Armstrong, A.T., 1976. Porphyry copper deposits of the alkalic suite: Galore Creek, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 402-414. Barr, D.A, Fox, P.E., Northcote, K.E. and Preto, V.A., 1976. The alkaline suite porphyry deposits; a summary, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 359-367. Burnham, C.W., 1985, Energy release in subvolcanic environments: implications for breccia formation: Economic Geology, v. 80, p. 1515-1522. Byrne, K., 2009. The Southwest Zone breccia-centered silica-undersaturated alkalic porphyry Cu-Au deposit, Galore Creek, B.C: Magmatic-hydrothermal evolution and zonation, and a hydrothermal biotite perspective. Vancouver, University of British Columbia, M.Sc. thesis, 170 p. Byrne, K., Tosdal, R.M., and Simpson, K.A., 2010, Coherent and clastic rocks in the Southwest Zone alkalic porphyry Cu-Au system, Galore Creek, Canada (NTS 104G): Geoscience BC Summary centered Cu-Au alkalic porphyry: Southwest Zone, Galore Creek: Economic Geology. Colpron, M., Nelson, J.L., and Murphy, D.C., 2007, Northern Cordilleran terranes and their interactions through time: GSA Today, v. 17, no. 4/5, p. 4-9. Coney, P.J., 1989, Structural aspects of suspect terranes and accretionary tectonics in western North America: Journal of Structural Geology, v. 11, p. 117-125. Cooke, D. R., Wilson, A. J., House, M. J., Wolfe, R. C., Walshe, J. L., Lickfold, V. and Crawford, A. J., 2007, Alkalic porphyry Au - Cu and associated mineral deposits of the Ordovician to Early Silurian Macquarie Arc, New South Wales: Australian Journal of Earth Sciences, v. 54:2, p. 445-463. Davies, A.G.S., Cooke, D.R., Gemmell, J.B., and Simpson, K.A., 2008b, Diatreme breccias at the Kelian gold mine, Kalimantan, Indonesia: precursors to epithermal gold mineralisation: Economic Geology, v. 103, p. 717-757. Enns S.G., Thompson, J.F.H., Stanley, C.R. and Yarrow, E.W., 1995. The Galore Creek porphyry copper-gold deposits, northwestern British Columbia in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordillera of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 640-644. Hedenquist, J.W. and Henley, R.W., 1985, Hydrothermal eruptions in the Waiotapu geothermal system, New Zealand: their origin, associated breccias, and relation to precious metal mineralization: Economic Geology, v. 80, p. 1640-1668.  54  Lang, J.R., Thompson, J.F.H., and Dunne, K.P.E., 1993, Hydrothermal garnet from the Galore Creek Cu-Au porphyry deposit, B.C. Canada: Implications of geochemical and fluid inclusion zoning patterns: Geological Society of America Abstracts with Program, v. 25, p. A-402. Lang, J.R., Stanley, C.R, and Thompson, J.F.H, 1995c, Na-K-Ca magmatic hydrothermal alteration associated with alkalic porphyry Cu-Au deposits, British Columbia in Porphyry Copper Deposits of the American Cordillera, F.W. Pierce and J.G. Bolm (ed.), Arizona Geological Society, Digest 20, p. 219-236. Logan, J.M., 2005, Alkaline magmatism and porphyry Cu-Au deposits at Galore Creek, northwestern British Columbia: B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2004, Paper 2005-1, p. 237-248, URL <http://www.empr.giv.bc.ca/Mining/ Geoscience/PublicationCatalogue/Fieldwork/Pages/GeologicalFieldwork2004.aspx> [May, 2010]. Logan, J.M., 2007, The progression from damage to localization of displacement observed in laboratory testing of porous rocks: Geological Society Special Publications, v. 289, p.7587. Logan, J.M., Koyanagi, V.M., and Rhys, D.A., 1989b, Geology and mineral occurrences of the Galore Creek Area (104A and B): B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1989-8. Logan, J.M., and Koyanagi, V.M., 1994, Geology and mineral deposits of the Galore Creek area, northwestern British Columbia (104G/3 and 4): BC Ministry of Energy, Mines, and Petroleum Resources, Bulletin 92, 96 p. McCallum, M.E., 1985, Experimental evidence for fluidization processes in breccia pipe formation : Economic Geology, v. 80, p. 1523-1543. McMillan, W.J, 1991, Tectonic evolution and setting of mineral deposits in the Canadian Cordillera in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, BC Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, p. 1, URL <http://www.empr.gov.bc.ca/Mining/ Geoscience/PublicationsCatalogue/Papers/Pages/1991-4.aspx> [May, 2010]. McPhie, J., Doyle, M., and Allen, R., 1993, Volcanic texture: a guide to interpretation of textures in volcanic rocks: CODES Key Centre, University of Tasmania. Mihalynuk, M.G., Nelson, J., and Diakow, L.J., 1994, Cache Creek Terrane entrapment; oroclinal paradox within the Canadian Cordillera: Tectonics, v. 13, p. 575-595. Monger, J.W.H., 1977. Upper Palaeozoic rocks of the western Canadian Cordillera and their bearing on Cordilleran evolution: Canadian Journal of Earth Sciences, v. 14, p. 18321859. 55  Monger, J.W.H., and Irving, E., 1980, Northward displacement of north-central British Columbia: Nature, v. 285, p. 289-294. Monger, J.W.H., Price, R.A., and Tempelman-Kluit, D.J., 1982, Tectonic accretion and the origin of two major metamorphic and plutonic welts in the Canadian Cordillera: Geology, v. 10, p. 70-75. Monger, J.W.H, Wheeler, J.O, Tipper, H.W., 1992. Upper Devonian to Middle Jurassic assemblages: Cordilleran terranes (modified): Geological Society of America, G-2, p. 281-317. Mortensen, J.K., Ghosh, D. and Ferri, F., 1995. U-Pb age constraints of intrusive rocks associated with copper-gold porphyry deposits in the Canadian Cordillera, in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordilla of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 142-158. Mortimer, N., 1987. Late Triassic and Early Jurassic subduction-related volcanism in British Columbia. Canadian Journal of Earth Sciences, v. 24, p. 2521-2536. Nelson, J. and Colpron, M., 2007. Tectonics and metallogeny of the British Columbia, Yukon and Alaskan Cordillera, 1.8 Ga to present, in Goodfellow, W. D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Special Publication 5, Mineral Deposits Division, Geological Association of Canada, p.755-791. Nelson, J.L., and Mihalnyuk, M., 1993, Cache Creek ocean: closure or enclosure: Geology, v. 21, p. 173-176. NovaGold Resources Inc., 2008. NovaGold Expands Galore Creek Resource Estimate, URL <http://www.novagold.com/upload/pdf/NGReserve_ResourceTable.pdf> [June, 2008]. Panteleyev, A., 1976, Galore Creek map-area in Geological Fieldwork, 1975, BC Ministry of Energy. Mines and Petroleum Resources, Paper 1976-1, p. 79-81, URL <http://www.empr.gov.bc.ca/ Mining/Geoscience/PublicationsCatalogue/Fieldwork/Pages/GeologicalFieldwork1975.a spx> [May, 2010]. Schwab, D. L, Petsel, S., Otto, B. R., Morris, S. K., Workman, E. and Tosdal, R. M., 2008, Overview of the Late Triassic Galore Creek Copper-Gold-Silver Porphyry System, in Spencer, J.W., and Titley, S.R., eds., Ores and orogenesis: Circum-Pacific tectonics, geologic evolution and ore deposits: Tucson, Arizona Geological Society Digest 22, p. 471-484. Seedorff, E., Dilles, J. H., Proffett, J. M., Einaudi, M. T., Zurcher, L., Stavast, W. J. A., Johnson, D. A., and Barton, M. D., 2005, Porphyry Deposits: Characteristics and Origin of Hypogene Features: Economic Geology, 100th Anniversary Volume, p. 251-298.  56  Sheridan, M.F., and Wohletz, K.H., 1981, Hydrovolcanic explosions: the systematic of waterpyroclast equilibration: Science, v. 212, p. 1387-1389. Sillitoe, R.H., 1985, Ore-related breccias in volcanoplutonic arcs: Economic Geology, v. 80, p. 1743-1774. Souther, J.G., Manger, J.W.H., and Gabrielse, H., 1971, Late tectonic evolution of the Canadian Cordillera in Abstracts with Programs: Geological Society of America, v.3, no.7, p.714. Ulrich, T., Gunther, D., and Heinrich, C.A., 2001, The evolution of a porphyry Cu-Au deposit, based on LA-ICP-MS analysis of fluid inclusions of fluid inclusions: Bajo de la Alumbrera, Argentina: Economic Geology, v. 96, p. 1743-1774. Wernicke, B., and Klepacki, D.W., 1988, Escape hypothesis for the Stikine block: Geology, v. 16, p. 461-464. Wilson, A. J., Cooke, D. R., and Harper, B., L., 2003, The Ridgeway gold–copper deposit: a high-grade alkalic porphyry deposit in the Lachlan Fold Belt, New South Wales, Australia: Economic geology, v. 98, p. 1637-1666.  57  3  Hydrothermal alteration and mineralization of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada2  3.1 Introduction Two general classes of auriferous porphyry Cu deposits are recognized; those associated with calc-alkalic magmatic rock and those associated with alkalic magmatic rocks (Sillitoe, 2000; Seedorff et al., 2005). Many of the gold-rich porphyry Cu deposits are associated with intrusions of alkalic or shoshonitic magmatic affinity (Jensen and Barton, 2000; Sillitoe, 2000; Wilson et al., 2003, 2007). The alkalic-type porphyry Cu-Au systems also consist of two broad petrologic families of intrusion; those that are associated with silica saturated, or those with silica undersaturated alkalic intrusive complexes (Lang et al., 1995a).  The most notable  differences between them is the presence or absence of quartz veins, which are common in the porphyry systems associated with silica saturated alkalic complexes such as those located in the upper Ordovician to lower Silurian Lachlan Fold Belt, New South Wales, Australia (Wilson et al., 2003; Cooke et al., 2007) or the Triassic Red Chris deposit in British Columbia (Baker et al., 1999). Quartz veins are notably absent or, at best, very sparse in porphyry systems associated with silica undersaturated intrusive complexes, such as those common in the upper Triassic to lower Jurassic Quesnell or Stikine terranes of British Columbia, Canada (Barr et al., 1976; Lang et al., 1995a). As a class, some auriferous porphyry Cu deposits contain Au and Cu concentrations that equal to or are greater than the combined metal content of many of their calc-  2  A version of this chapter has been submitted for publication. Micko, J., Tosdal, R.M., Bissig, T., Chamberlain, C.M., and Simpson, K.A. (2010) The Hydrothermal alteration and mineralization of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada.  58  alkalic cousins. However, as a family, the alkalic porphyry Cu-Au systems are less well known and recognized on a global basis. Although similar in many respects to the calc-alkalic porphyry Cu-Au system, alkalic porphyry Cu-Au deposits differ significantly in some respects. The Galore Creek district in northwestern British Columbia, about 100 km northeast of Wrangell, Alaska (Fig. 3.1), is one of three undeveloped porphyry Cu-Au districts in the Stikine Terrane. The other two are Schaft Creek and Red Chris. Galore Creek has many unusual features and is arguably the end-member example of the silica-undersaturated class of alkalic porphyry Cu-Au deposits (Lang et al., 1995b). The district contains five explored prospects and six other mineralized centers with only limited exploration.  The prospects define a five kilometers long, northwesterly trending  corridor. A mineralized satellite prospect at Copper Canyon lies about six kilometers east of the Galore Creek valley, but the relationship to the Galore Creek cluster is uncertain. The largest prospect at Galore Creek is the Central Zone (CZ), the focus of this paper. It contains three adjacent and overlapping mineralized centers: the North Gold Lens (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL). In addition, another mineralized center, the Bountiful Zone (Fig. 3.2), underlies the SGL; this zone is beyond the scope of this study, but peripheral alteration from the zone is present in the mapped areas (see below).  59  Figure 3.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing location of the Galore Creek Copper porphyry Au-Cu district and other porphyry Cu centers. Red Box outlines the area shown in figure 1B. B) Regional geology of the northwestern Stikine Terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994).  60  Figure 3.2: A) Interpreted surface bedrock geology of the Central Zone showing location from three E-oriented cross-sections and one N-oriented long section that crosscut the three principal mineralized centers of the North Gold Len (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL). Also shown is the location of the deep Bountiful Zone (BZ). Geology modified after NovaGold Resources Inc. (2007). B) Surface alteration and sulfide mineral distribution of the Central Zone. Geologic contacts in panel A reproduced as gray lines for reference. Map modified from Schwab et al. (2008).  61  The CZ was discovered based on an aeromagnetic survey in the late 1950’s. Since the early 1960s, Stikine Copper Ltd., Kennecott Canada Inc., and recently NovaGold Resources Inc., have explored the district. The Galore Creek Mining Cooperation, an equal partner joint venture between NovaGold Resources Inc. and Teck Resources Ltd., has operated the property since 2007. As of 2008, the combined measured and indicated resources at Galore Creek are 785.7 million tonnes grading at 0.52% Cu, 0.29g/t Au and 4.87g/t Ag (NovaGold Resources Inc., 2008). In this manuscript, we document the hydrothermal evolution of the CZ deposit based on the lithological architecture, hydrothermal alteration assemblages and sulfide zonation patterns. This information, together with new U-Pb geochronology constraints on hydrothermal titanite, is integrated into an evolutionary ore deposit model for the CZ. Byrne (2009) and Schwab et al. (2008) describe the other mineralized centers in the Galore Creek district.  3.2 Regional geology and tectonic setting The Cordilleran tectonic collage of British Columbia contains the largest concentration of alkalic porphyry Cu-Au deposits and prospects in the world. The deposits and prospects are scattered over the 1500 km strike length of the Late Triassic and Early Jurassic magmatic arc that composes the inboard Quesnell and outboard Stikine terranes (Fig. 3.1A). The Quesnell and Stikine terranes represent distinct segments of an extensive marine island arc system, which currently encloses the oceanic Cache Creek accretionary complex due to Early Jurassic oroclinal bending that accompanied progressive amalgamation of the marine arcs to North America (Mihalynuk et al., 1994; Nelson and Colpron, 2007; Colpron et al., 2007). Metallogenic belts in these terranes (Fig. 3.1) are (1) the Late Triassic calc-alkaline plutonic complexes that have associated porphyry Cu-Mo(±Au) deposits (Schaft Creek, Highland Valley, and Gibraltar), (2) 62  the slightly younger, Late Triassic alkalic diorite to monzonitic intrusive complexes associated with porphyry Cu-Au deposits (Galore Creek, Red Chris, Afton/Ajax, Copper Mountain and Mt. Polley), and (3) the Middle Jurassic alkalic intrusive complexes with associated porphyry Au-Cu deposits (Lorraine, Mount Milligan) (Barr et al., 1976; Lang et al., 1995a; Mortensen et al., 1995; Logan et al., 2005; Scott et al., 2008). Most silica-undersaturated alkalic porphyry Cu-Au deposits were emplaced in a relatively short episode between 210 and 200 Ma, after the end of widespread tholeiitic to transitional calc-alkaline magmatic activity (Mortimer, 1987; Mortensen et al., 1995; Logan et al., 2007; this study). After a hiatus of 10 to 15 million years, which corresponds to a major Cordilleran-long shortening and deformation event (Monger et al., 1992; Mortensen et al., 1995), early Jurassic (180-190 Ma) alkalic porphyry Cu-Au deposits such as Lorraine and Mt. Milligan (Mortensen et al., 1995; Jago, 2008) were emplaced in north-central British Columbia.  3.3 District geology The Galore Creek district, located at the northwestern margin of the Stikine terrane (Fig. 3.1A), is hosted within the lower Devonian to upper Permian Stikine assemblage and the lower to upper Triassic Stuhini Group (Fig. 3.1B). The oldest rocks of the Stikine assemblage lying northeast of Galore Creek (Fig. 3.1B) are strongly deformed Devonian to Permian limestones, interbedded with mafic and intermediate lavas and volcaniclastic units, as well as a thin succession of middle Triassic siltstones, sandstones, and cherts (Monger, 1977; Enns et al., 1995; Logan, 2005). Unmetamorphosed rocks of the upper Triassic Stuhini group underlying the Galore Creek valley (Fig. 3.2) are subdivided into a lower unit of submarine basaltic to andesitic volcanic rocks interspersed with locally derived sandstones and siltstones (Allen et al., 1976) and an upper unit of partially subaerial, compositionally distinct alkali-enriched volcanic and 63  volcanogenic sedimentary rocks (Fig. 3.3). The Stuhini Group rocks host the Late Triassic alkalic intrusive complex and the related hydrothermal systems.  Figure 3.3: Regional stratigraphy and volcanic to volcaniclastic facies interpretation of the Galore Creek upper Triassic successions in the Central Zone. Modified after Logan and Koyanagi (1994).  The Galore Creek district lies in the footwall of a west-directed brittle thrust fault (not shown on figure 3.2A) that superposes tightly folded and weakly metamorphosed rocks of the Stuhini Group over petrologically similar rocks in the footwall that host the porphyry Cu-Au systems (Logan 2005; Schwab et al., 2008). Small displacement reverse faults cut the Stuhini Group rocks, the intruding syenite and monzonite intrusions, and the porphyry Cu-Au centers (Fig. 2A; Schwab et al., 2008; Byrne, 2009). Sedimentary rocks equivalent to the lower Jurassic Hazelton Group that postdate mineralization are preserved north and east of Galore Creek, as are the lower Jurassic to lower  64  Tertiary successor-basin sedimentary rocks of the Bowser Lake and Sustut Groups (Fig. 3.1B; Allen et al., 1976; Logan, 1989a, b; Enns et al., 1995). Steeply inclined (60° to 75º westerly dip) Eocene quartz monzonite and diorite stocks, as well as mafic to felsic dykes of unknown age, intrude the Triassic rocks throughout the CZ. These young dykes are concentrated in west- and north-striking zones that presumably exploited a fault or fracture mesh (Enns et al., 1995).  3.4 Central Zone geology The three mineralized centers of the CZ, the NGL, CRZ, and SGL (Fig. 3.2A), are up to 350 to 500m wide, 400m to 700m deep (current exploration depth) and covered by 10 to 80m of Quaternary glacial deposits. The upper 10 to 100 m of bedrock is fragmented due to the hydration and dissolution of an anhydrite-filled fracture-mesh. To constrain the geological architecture and hydrothermal evolution of the CZ deposits, three subparallel east-oriented vertical sections and one north-oriented, vertical long section crossing the dominant ore-bearing regions were relogged (Figs. 3.2 and 3.4) using 24 diamond drill holes, totaling 12,495 meters of core. These data are augmented by the exploration database.  65  Figure 3.4: Distribution of rocks in the A) North Gold Lens (section 6335547), B) Central Replacement Zone (section 6335100); and C) the South Gold Lens (section 6334100). Section location is in figure 3.2A.  66  3.4.1  Supracrustal hostrocks  Volcanic and volcaniclastic rocks of the middle to upper Triassic Stuhini Group throughout the Central Zone generally strike west-northwesterly and dip 45° to 60º S-SW (Figs. 3.2A, 3.4, and 3.5). The stratigraphically oldest units are only intersected at depth in the NGL (Figs. 3.4A and 3.5). Fine-grained sandstone to siltstone and ribbon chert, characterized by its distinct planar laminations, form the stratigraphically lowest unit. These rocks are extensively hydrothermal altered (Fig. 3.6A), thereby precluding any additional knowledge of their protolith.  Figure 3.5: Distribution of rocks along a vertical N-oriented long section 351000 through the three mineralized zones composing the Central Zone. Section location is in figure 3.2A.  67  Figure 3.6: Late Triassic Stuhini Group and intrusive units in the Central Zone. A) Lower to middle Triassic phyllite and ribbon chert with disseminated bornite and chalcopyrite distributed along laminations; GC06-0734 (795.00m), NGL, potassic 2a. B) Augite-phyric basaltic conglomerate; GC05-0702 (205.33m), NGL, potassic and calcic 2b. C) Fluidally-shaped pseudoleucite-phyric clasts in volcaniclastic sandstone (peperite); pseudoleucite phenocrysts are locally replaced by biotite, chalcopyrite and pyrite; GC04-0448 (537.50m), SGL, potassic 1 and 2a. D) Orthoclase-phyric trachyte (subvolcanic intrusion); GC05-0734 (590.00m), NGL, potassic 2a. E) Orthoclase and pseudoleucite-phyric syenite crosscut by a garnet and chalcopyrite vein; GC06-0732 (297.36m), potassic 2a and calcic 2b. F) Orthoclase-phyric syenite; GC03-0441 (319.13m), SGL, potassic 3a. G) Megacrystic orthoclase and plagioclase-phyric monzonite locally replaced by late garnet; GC05-0537 (395.45m), NGL, potassic 2d and calcic 4b. H) Orthoclase-phyric monzonite crosscut by microfractures with orthoclase (or) selvages; GC06-0721 (277.70m), SGL, potassic 3a. I) Polymictic rock flour matrix breccia (SGL); GC04-0448 (275.00m), potassic 2a. J) Polylithic, pyroxene-anhydrite-cemented breccia (SGL); GC06-0721 (158.60m), calcic 3b and propylitic 4d. Mineral abbreviations: an, anhydrite; aug, augite; cpy, chalcopyrite; dp, diopside; epi, epidote; gar, garnet; or, orthoclase; ps, pseudoleucite; py, pyrite.  68  The sedimentary rocks are overlain conformably by subalkaline hornblende and plagioclase-phyric basaltic andesite rocks (Figs. 3.3, 3.4, and 3.5) that include both coherent and clastic facies. Subvolcanic intrusions or lavas are characterized by flow-aligned feldspar and hornblende phenocrysts in a groundmass of chlorite and feldspar. Polylithic volcanic conglomerate is dominated by hornblende- and plagioclase-phyric basaltic andesite clasts, but also contain sparse orthoclase-phyric and granitic clasts in a fine-grained matrix. Basaltic andesite units are conformably overlain by sub-alkaline to alkaline augite-phyric basaltic rocks. Lavas and/or sub-volcanic intrusions dominate, and contain abundant augite phenocrysts in a groundmass of augite and plagioclase (Fig. 3.6B). Less abundant volcanic conglomerate is monolithic, and characterized by augite-phyric basalt clasts in a fine-grained matrix. Pseudoleucite-phyric trachyte and derivative clastic rocks are volumetrically the most significant component of the Stuhini Group (Figs. 3.4 and 3.5), and host most of the Cu-Au at Galore Creek. These rocks conformably overlie the mafic volcanic rocks and include volcanogenic siltstones, sandstones, conglomerates and breccias. Sub-volcanic intrusions crosscut the older mafic volcanic rocks and the trachyte-derived clastic rocks. Extensive hydrothermal alteration generally masks the primary mineralogy of the trachyte. Planar lamination and syn-sedimentary slump structures characterize the clastic units. Also present are fluidally-shaped pseudoleucite-phyric clast breccias that are interpreted to be peperite derived from coeval sub-volcanic intrusions (Fig. 3.6C). Orthoclase-phyric trachyte in the NGL and SGL forms subvolcanic intrusions (Figs. 3.4 and 3.5) composed of abundant flow-oriented, tabular orthoclase phenocrysts embedded in a grey, fine grained to aphanitic orthoclase dominated groundmass (Fig. 3.6D).  69  3.4.2  The Central Zone intrusive complex  The CZ intrusive complex consists of compositionally variable intrusive units that are associated with the development of the hydrothermal system in the CZ and a number of satellite deposits throughout the Galore Creek district. In the CZ, the commonly tabular intrusions dominantly strike north-northwest and dip 45° to 60º west-southwest. The intrusions in the eastoriented sections appear generally sub-parallel to the stratigraphy (Fig. 3.4), but at high angles to stratigraphy in the north-oriented long section (Fig. 3.5). Fringing the CZ on the west and forming the host rock to the Southwest zone (Byrne et al., 2010) is a large, composite megacrystic orthoclase and plagioclase phyric monzonite stock (Fig. 3.2A). Concordant megacrystic monzonite sills emanate from the stock into the host supracrustal stratigraphy and the CZ ore body (Fig. 3.2A). Four principal intrusion types are defined based on petrology and crosscutting relationships. Each type has several textural varieties characterized by minor mineralogical variations such as phenocryst size and abundance. Orthoclase and pseudoleucite-phyric syenites are the oldest, and are characterized by a bimodal phenocryst population of orthoclase and pseudoleucite in a grey, “salt and pepper” textured groundmass that consists of fine-grained orthoclase and biotite (Figs. 3.6E and 3.6F). These orthoclase and pseudoleucite-bearing syenites are followed by younger orthoclase-phyric syenites that are very similar in composition, but lack pseudoleucite phenocrysts. Whilst this paragenetic relationship between the units could not be discerned within the examined drill-core, field and core logs by the company geologists have recorded the cross-cutting relationship between the two units throughout the CZ (Figs. 3.4 and 3.5). Megacrystic orthoclase and plagioclase-phyric monzonite is volumetrically the most abundant intrusive unit. It crosscuts the supracrustal hostrocks and orthoclase and pseudoleucite-  70  phyric syenites, particularly in the west and south of the CZ (Figs. 3.2A, 3.4, and 3.5). The unit is characterized by large tabular orthoclase phenocrysts and a secondary and smaller population of plagioclase phenocrysts in a grey to green, coarse-grained groundmass of feldspar, biotite, hornblende, and magnetite (Fig. 3.6G). Orthoclase-phyric monzonites are the youngest intrusive units, and are localized in the SGL, where they crosscut megacrystic orthoclase and plagioclase-phyric monzonite (Figs. 3.5C and 3.6H). These monzonites are characterized by a fine to medium grained groundmass of dominantly plagioclase, biotite, and magnetite. Locally, the monzonite intrusions contain abundant orthoclase-phyric syenite xenoliths (Fig. 3.6H). Texturally, they appear similar but finer grained to the megacrystic orthoclase and plagioclase-phyric monzonites, and are probably genetically related. Chronologic constraints on the CZ intrusive complex suggest at least three ages of intrusion. Mortensen et al. (1995) reported a U-Pb zircon age of 210±1 Ma for the orthoclase and pseudoleucite-phyric syenites, a 205±2.3 Ma age for zircon and 205±1.8 Ma for a titanite-K feldspar U-Pb isochron age for the megacrystic orthoclase and plagioclase-phyric monzonite. Titanite from the same rock unit gave a U-Pb age of 200±1.2 Ma, which may reflect the time of cooling below ~500°C, the lowest inferred Pb retention temperature for titanite (Cherniak, 1993; Frost et al., 2000; Schoene and Bowring, 2007). A late intrusion post-dating mineralization in the CZ has a titanite-K feldspar U-Pb isochron age of 197.2±1.2 Ma (Mortensen et al., 1995). 3.4.3  Breccias  In general, the breccia bodies have an inclined, pipe-like geometry consisting of variable proportions of clast, matrix and cement. To simplify, hydrothermal cement/alteration assemblages are described below.  71  The smallest breccia body located in the center of the SGL (Fig. 3.4C) is a polymictic matrix breccia characterized by sub-angular to sub-rounded clasts of orthoclase and pseudoleucite-phyric syenite and planar laminated alkaline volcanogenic sedimentary rock (60%) in a sand- to granule-sized matrix (Fig. 3.6I). The overall morphology and orientation of this breccia body has not been defined by drilling. A dominantly polymictic garnet-biotite-anhydrite cemented breccia is centered in the western portion of the CRZ and represents the largest of the breccia bodies (Figs. 3.4 and 3.5). Clasts types are pseudoleucite-phyric trachyte, associated volcaniclastic rocks, and orthoclase and pseudoleucite-phyric syenites. In the deep western portion of the breccia, black aphanitic clasts with whispy margins are interpreted to be juvenile, and were likely sourced from a magma associated with brecciation (Davies et al., 2008b). The breccia is internally zoned with a more polymictic, finer grained core and a monomictic jigsaw-fit facies on the eastern and upper margins. The cement to clast ratio changes from 1:20 near the margin, to 1:5 and 1:1 in the center of the breccia body. A dominantly polymictic, pyroxene-biotite-magnetite-cemented breccia body is located in the western portion of the NGL (Figs. 3.4A and 3.5). Clasts types are pseudoleucite-phyric trachyte, orthoclase and pseudoleucite-phyric syenites, orthoclase-phyric syenite, and augitephyric basalt. The breccia body is internally zoned with a more polymictic, finer grained core and monomictic jigsaw-fit facies along the margins. The cement to clast ratio changes from 1:5 near the top margin to 1:1 in the center of the breccia body. Breccia textures and clast and cement compositions (see below) are similar to the polymictic garnet-biotite-anhydrite cemented breccia of the CRZ. A polymictic, magnetite, biotite, and pyroxene-anhydrite cemented breccia body occurs in the western portion of the SGL (Figs. 3.4C and 3.6J). Clasts are exclusively orthoclase-phyric  72  monzonite and associated igneous-cemented breccia (Davies et al., 2008b). The angular clasts and commonly jigsaw-fit clast organization implies brecciation with minimal clast transport (Fig. 3.6J). The breccia morphology and size is uncertain, as the western margin remains undefined by drilling. A fault dipping steeply ~70° to the west forms the eastern margin. There is no discernable zonation within the breccia, but the characteristics are similar to a hydrothermal breccia described in the Southwest Zone (Byrne et al., 2010).  3.5 Hydrothermal alteration Hydrothernmal minerals identified in the Central Zone are grouped into five main assemblages (Table 3.1) in accordance with the classic schemes devised and summarized by Lowell and Gilbert (1970), Titley (1982) and more recently Sillitoe (2010). Table 3.1 Hydrothermal alteration assemblages observed in the Central Zone. Both dominant and subordinate minerals were defined on the basis of macroscopic and microscopic observations backed up by SEM and EMP. Alteration assemblage  Dominant minerals  Subordinate minerals  Potassic  Orthoclase, biotite, magnetite, hematite  Anhydrite, apatite  Calcic  Garnet, pyroxene  Anhydrite, titanite, barite, celestite  Sodic  Albite  SAC (phyllic)  Sericite, anhydrite, calcite  Pyrite  Propylitic  Epidote, chlorite  Anhydrite, pyrite, siderite, ankerite  rutile,  apatite,  Characteristic mineralogy, texture and crosscutting relationships of the alteration assemblages observed are described from oldest to youngest for each mineralized center. Reappearing alteration assemblages are described once in detail, and referred to where appropriate in the other mineralized centers. The complex alteration history and the spatial overlap of individual alteration and mineralized zones prohibit the construction of maps that show the distribution of individual alteration sub-stages. Thus, composite sections show only the 73  dominant alteration minerals representing the principal alteration assemblages, sulfide minerals and Cu-Au distribution (see below). 3.5.1  Hydrothermal paragenesis of the North Gold Lens (NGL)  Early stage alteration Potassic 1: Early stage potassic 1 alteration is rare in the NGL, except in the easternmost part of the pseudoleucite-phyric trachyte unit, where younger overprinting alteration is weak. White orthoclase and fine-grained, shreddy black biotite is either pervasive or form selvages to irregularly oriented micro-fractures (Fig. 3.7A). No associated sulfides are known. Potassic 1 stage is distinguished from younger potassic alteration stages by the lack of hematite dusting in orthoclase and the preservation of host rock textures.  74  75  Figure 3.7: Hydrothermal alteration stages and associated textures in the Central Zone. Galore Creek is a silicaundersaturated magmatic-hydrothermal system and thus lacks (quartz-) veins and stockwork development. Where crosscutting relationships between individual alteration assemblages have been observed photographic evidence is provided in this figure. Several alteration stages, however, were defined on the basis of crosscutting and timing relationships between rock units, i.e intrusions and breccias. The presence or absence of a specific alteraration assemblage in one unit provides a relative paragenetic sequence despite the lack of distinct overprinting relationships. The reader is thus refered to section 3.4 and chapter 2, Tables 2.2 to 2.4. A) Fresh orthoclase-phyric trachyte crosscut by orthoclase-bearing veins of potassic (pot) stage 1; GC05-0568 (179.50m), NGL B) Orthoclasephyric trachyte pervasively altered by texturally non-destructive orthoclase of potassic stage 1, crosscut by biotite and magnetite-bearing veins of potassic stage 2a; GC06-734 (367.00m), NGL. C) Pseudoleucite-phyric syenite pervasively altered by orthoclase of potassic stage 1, crosscut by biotite and chalcopyrite-bearing veins of potassic stage 2a. Pseudoleucite phenocrysts are replaced by biotite and chalcopyrite preserving the original crystal shape; GC05-0514 (238.50m), NGL. D) CRZ breccia: Pseudoleucite-phyric syenite derived clast pervasively altered by potassic stages 1 and 2, cemented by garnet, biotite and anhydrite of calc-potassic (calc-pot) stage 2b; GC06-0732 (294.00m), CRZ. E) Orthoclase-phyric trachyte replaced by texturally non-destructive orthoclase of potassic stage 1, overprinted by orthoclase and biotite-bearing alteration of potassic stage 2a, crosscut by coarse, pegmatitic orthoclase and biotite bearing vein of potassic stage 2c; GC06-0734 (363.70m), NGL. F) Hornblende and plagioclase-phyric basaltic andesite replaced by finely disseminated diopside, biotite and magnetite of calc-potassic stage 2b, crosscut by coarse, pegmatitic orthoclase, biotiten and anhydrite bearing vein of potassic stage 2c; GC060734 (314.00m), NGL.) G) Megacrystic orthoclase and plagioclase-phyric monzonite is crosscut and pervasively altered by texturally destructive orthoclase of potassic stage 2d; GC05-0637 (469.00m), SGL. H) SGL breccia: Orthoclase-phyric monzonite clasts pervasively altered by texturally non-destructive orthoclase and minor biotite of potassic stage 3a and cemented by diopside and anhydrite of calcic stage 3b; GC05-0637 (158.60m), SGL. I) SGL breccia: Orthoclase-phyric trachyte derived clasts replaced by several stages of potassic alteration and cemented by magnetite and biotite of potassic stage 3b; GC05-0637 (159.50m), SGL. J) SGL breccia cemented by alteration assemblages of calc-potassic stage 3b overprinted by pervasive, texturally destructive orthoclase of potassic stage 3c and crosscut by siderite (sid) vein of propylitic stage 4d; GC05-0637 (216.15m), SGL. K) Orthoclase-phyric syenite replaced by texturally destructive albite (alb) alteration. Chalcopyrite and bornite may have been deposited prior to or syn-sodic alteration; GC06-0721 (447.40m), SGL. L) Megacrystic orthoclase and plagioclase-phyric monzonite pervasively altered by texturally non-destructive orthoclase and biotite of potassic stage 2d as well as small accumulations of garner of calcic stage 4b; GC05-0637 (395.45m), SGL. M) Unknown hostrock in the vicinity of the South Fault, texturally obliterated by coarse crystalline orthoclase and overprinted by sericite (ser) that is composed of white muscovite (mus) and fuchsite (fuch) associated with Sericite-Anhydrite-Carbonate (SAC) alteration stage 4c; GC05-0637 (398.40m), SGL. N) Augite-phyric basalt crosscut by sericite and calcite-vein of SAC stage 4c and overprinted by pervasive chlorite alteration of propylitic stage 4d; GC05-0702 (267.10m), NGL.  76  Main stage alteration Potassic 2a: The strong potassic stage in the CZ is present in the west and center of the NGL (Figs. 3.8A, 3.8B, 3.9B, 3.9A, and 3.10B). Light grey to pink, texture destructive orthoclase, coarse black biotite, disseminated magnetite, specular hematite, anhydrite, and apatite form the assemblage that forms pervasive and vein-style atlteration (Figs. 3.7B and C). Where present chalcopyrite and bornite are generally disseminated, and replace biotite and magnetite. Bornite also replaces specular hematite. A common observation within potassic stage 2a as well as other alteration stages described below is that sulfides appear to form last in the precipitation sequence. Potassic assemblage 2a and associated sulfides appear better developed in the felsic rock units. The assemblage affects the pseudoleucite-phyric subvolcanic intrusions (Fig. 3.7C), but does not alter the orthoclase-and pseudoleucite-phyric syenites, thus, suggesting that latter intrusions post-date potassic 2a.  77  Figure 3.8: Distribution of alteration mineral assemblages in the CZ along the vertical long section 351000. View represents an oblique cut through the eastward tilted hydrothermal systems. A) Orthoclase and specular hematite distribution; B) biotite and magnetite distribution; C) calcic alteration; D) SAC and propylitic alteration assemblages.  78  Figure 3.9: A) Sulfide and alteration assemblage distribution and B) metal zonation of the CZ along the vertical long section 351000. View represents an oblique cut through the eastward tilted hydrothermal systems.  79  80  Figure 3.10: Distribution maps of the four alteration types and associated assemblages in the NGL along section 6335547 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.02.0 g/t Au).  81  Several distinct textures characterize potassic 2a. Felsic rocks are strongly orthoclase altered to a pale pink to red color, because of hematite dusting (Figs. 3.6D). Where biotite, magnetite or specular hematite, and anhydrite are dominant over orthoclase, felsic host rocks are a steel-grey to bluish color. In the mafic volcanic rock units, the dominant biotite and magnetite gives the rocks a dark green-brown to black color (Fig. 3.6B). In mafic volcaniclastic units, orthoclase forms thin (0.2 to 0.7cm wide), beige colored alteration rinds to clasts. Both primary and earlier alteration mineralogy, as well as primary rock textures, are obliterated where potassic alteration 2a is well developed. Locally, primary rock textures may be partly preserved. Primary pseudoleucite crystals are recognizable due to selective replacement by biotite, magnetite, specular hematite, and sulfide minerals (Fig. 3.7C). Calcic and potassic 2b: A diopside-biotite-magnetite-cemented breccia body (Fig. 3.7D) in the western part of the NGL localizes calcic and potassic 2b stage alteration (Figs. 3.6B, 3.8C, 3.9A, and 3.10A to 3.10C). The breccia cuts supracrustal rocks and syenites previously altered during potassic alteration 1 and 2a. The older calcic alteration assemblage extends beyond the limits of the hydrothermal breccia body. Within the breccia, the calcic alteration assemblage is characterized by pyroxene and minor garnet. Pyroxene, the dominant hydrothermal cement phase, formed fine crystalline aggregates that replaced or enveloped clasts, and locally developed elongated crystals (<0.5cm) infilling marginal fractures and cavities. Locally, pyroxene replaced garnet. Garnet formed fine crystalline aggregates and, rarely, well developed crystals (<0.8cm). Locally, garnet is replaced by small grains of barite, celestite, and apatite. Pyroxene is intergrown with by titanite or rutile. In the wall rocks of the breccia body, the calcic 2b alteration assemblage dominates the mafic volcanic rock units. Calcic alteration is pervasive and locally formed vein-style replacement. Veins are typically in close vicinity to the breccia body in the west of the NGL, and dip between 45 and 60ºW. The vein margins are commonly defined by coarse crystalline 82  pyroxene (1.5-2.7cm) that is zoned from a light green core to a dark green outer growth zone. Pyroxene in the wall rocks is locally replaced by honey-brown garnet, in contrasts to the overprinting relationships within the calcic assemblage in the breccia body. Within the mafic volcanic rock units, fine crystalline pyroxene pervasively replaces the groundmass, whereas garnet forms either fine grained, patchy replacement, or thin but distinct (0.2 to 0.7cm wide) alteration rinds around clasts. Potassic 2b, which is roughly confined to the hydrothermal breccia and fractures in the immediate wall rock, is younger than the calcic alteration. It is texturally destructive resulting in complete replacement of the host rock. It is characterized by abundant large crystals of biotite (>1cm), magnetite and rare orthoclase that locally replaced diopsidic pyroxene and garnet. A second mineralization event that introduces chalcopyrite and minor bornite is associated with potassic assemblage 2a. The sulfides preferentially replaced biotite and magnetite, and also formed the youngest hydrothermal cement in the hydrothermal breccia body and, to a lesser extent, the fractured margins and distal veins formed by calcic 2b. Potassic 2c: Sparsely distributed in the shallow western portion of the NGL, potassic 2c alteration does not pervasively alter the host rock unlike older potassic stages. Instead, the assemblage is characterized by two vein-styles. One vein type, found in the deep, western portion of the NGL, is dominated by large (>1.2cm) translucent, pale pink or purple orthoclase (> 1.2cm) surrounded by texture destructive selvages of one or more generations of fine grained, pale pink to white orthoclase (Figs. 3.7E and F). Locally, orthoclase is intergrown with coarse titanite, black biotite (<2cm) and rare chalcopyrite. A second vein type is composed exclusively of coarse, black biotite. The veins’ thickness can range from 0.5 to 100cm. No sulfide is recognized in association with the second vein type. Both vein types dip about 45 to 60ºW, subparallel to the general orientation of the host rock. They crosscut felsic rock units affected by  83  potassic 1 and 2a, as well as host syenites. The veins are not present in the breccia, nor where calcic and potassic 2b are developed. Potassic 2d: Pervasive and vein-style white to pale pink colored orthoclase, fine grained (shreddy) biotite and grains of magnetite defining potassic 2d are present throughout the NGL cutting the supracrustal host rocks, syenites and the hydrothermal breccia (Figs. 3.6G and 3.7G). Only minor disseminated chalcopyrite and pyrite is present. The alteration is spatially associated with, and appears genetically linked to, the megacrystic orthoclase- and plagioclase-phyric monzonites.  Due to mineralogical similarities with older potassic alteration assemblage,  distinguishing this event outside these intrusive bodies is difficult, especially where no distinct veins or alteration fronts are visible.  Late stage alteration Calcic 4b: Late stage alteration events crosscut or overprint all main stage alteration assemblages. The alteration is spatially restricted to the shallow eastern portion of the NGL, where it overprinted megacrystic orthoclase-phyric monzonites and mafic volcanic units (Fig. 3.10C). Garnet defines the assemblage. It is commonly red brown in color and formed either round clots (0.5-1cm) referred to as “oatmeal”-texture (Figs. 3.6G and 3.7L), or irregularly oriented micro-veinlets crosscutting the host rocks. Sericite-anhydrite-carbonate (SAC): In the western and eastern portions of the NGL (Figs. 3.8D and 3.10D), late sericite-calcite-anhydrite is spatially associated with megacrystic orthoclase and plagioclase-phyric monzonites. Sericite commonly has a pale green colour and has replaced plagioclase phenocrysts of the megacrystic monzonites, whereas calcite and anhydrite form small (mm-sized) veinlets that crosscut the host rock (Fig. 3.7N). Calcite and anhydrite also infill micro-fractures in garnet precipitated during the calcic 4b stage.  84  Propylitic: Chlorite, epidote, and pyrite dominate the eastern- and westernmost extensions of the NGL (Figs. 3.8D and 3.10D). Chlorite particularly dominates in mafic volcanic rocks and megacrystic monzonites, where it replaced biotite and hornblende (Fig. 3.7N). Epidote is minor and host rock controlled, being spatially restricted to megacrystic monzonites and adjacent mafic volcanic rock units. Epidote has replaced plagioclase and earlier garnet. Pyrite is restricted to mafic volcanic units, where it forms either 0.5 to 1cm wide irregularly distributed veins or large disseminated cubes (0.2 to 0.7cm) that have replaced biotite or magnetite. Sulfide mineral zonation A roughly ellipsoidal Cu (> 0.5-1.5% Cu) and Au (> 1.0-2.0g/t Au) shell defines the core of the NGL (Figs. 3.9B and 3.10F). The shell is 350m in width and 500m in length on the section plane, parallel to the apparent dip of the surpracrustal host rocks and intrusions. The gold-rich core of the mineralized shell is characterized by bornite + chalcopyrite, flanked outwards by a medial chalcopyrite domain passing into chalcopyrite + pyrite zone. The margins are dominated by pyrite.  Gold is principally associated with bornite, as is the case in many  porphyry Cu-Au deposits (e.g. Kesler et al., 2002; Seedorff et al., 2005). Two stages of sulfide precipitation in the NGL are recognized. Early disseminated bornite and chalcopyrite, introduced at the end of potassic 2a stage, contributed the bulk of the Cu and Au. The lower western extension of the ore shell correlates with the hydrothermal breccia body where a second sulfide stage is related to potassic alteration 2b (Fig. 3.10F). The second sulfide event is subordinate to the first. The overall Cu (%): Au (g/t) ratio observed in the NGL is 2:1 (Schwab et al., 2008).  85  3.5.2  Hydrothermal paragenesis of the Central Replacement Zone (CRZ)  The CRZ is generally characterized by the same sequence of hydrothermal alteration events as the NGL. However, the intensity of hydrothermal activity, some alteration stages, as well as the overall metal tenor, formed differently. Early and main stage alteration Potassic 1 and 2a: Main stage potassic alteration is best developed in the felsic rock units in the eastern parts of the CRZ (Figs. 3.8A, 3.8B, 3.11A, and 3.11B). In the center, the alteration assemblage is preserved as altered clasts in the hydrothermal breccia body. Mineralogical and textural characteristics of the alteration assemblages, sulfide deposition, and their crosscutting relationships are equivalent to those in the NGL.  86  87  Figure 3.11: Distribution maps of the four alteration types and associated assemblages in the CRZ along section 6335100 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.02.0 g/t Au).  88  Calcic and potassic 2b: An extensive garnet-biotite-anhydrite-cemented breccia formed during this sub-stage dominates the CRZ. The breccia is interpreted to be genetically and spatially related to the hydrothermal breccia body of the NGL (Figs. 3.4B and 3.5). In the CRZ, the breccia cuts felsic host rocks and syenites previously altered during potassic 1 and 2a stages. Both calcic and potassic 2b alteration assemblages are roughly confined to the breccia body and the fractured margins (Figs. 3.8C, 3.11A, and 3.11E). As in the NGL, calcic alteration predates potassic 2b alteration, and dominates the core and deeper sections of the breccia. However, in the CRZ, garnet is the principal cement phase with small, localized centers of diopsidic pyroxene primarily in the deep western section of the breccia body (Fig. 3.7D). Garnet locally forms fine crystalline aggregates either replacing the groundmass in the clasts or occurring as distinct alteration rinds on the clasts. More commonly, oscillatory zoned garnet infills fractures and cavities. Here, it formed large crystals up to 2cm in diameter with a dark brown, melilitic, and andraditic core surrounded by tan-colored grossularitic rims (Lang et al., 1993; Lange 1994; Russell et al., 1999; chapter 5). Bands of anhydrite and inclusions of barite, celestite, and apatite are also locally present. This zonation is also present in some garnets of the NGL. Diopsidic pyroxene in the CRZ forms a fine crystalline replacement of clasts or alteration rinds to clasts. Rare pyroxene forms large crystals (0.5 to 1cm) as fracture or cavity infill. The large, diopsidic pyroxene is zoned from a light green core to dark green rim, and is commonly intergrown with anhydrite, without accessory titanite and rutile. Diopsidic pyroxene has also locally replaced garnet. Potassic assemblage 2b dominates the central and eastern carapace of the breccia and surrounding fractured margin. The potassic alteration and cement assemblage 2b is similar to that in the NGL, except that coarse crystalline biotite (>1cm) is dominant over magnetite and orthoclase is rare. The second sulfide event associated with potassic alteration stage 2b is more prominent in the CRZ than in the NGL, but lacks associated bornite. Sulfide also formed a 89  separate cement phase with abundant anhydrite, infilling remnant open cavities within the hydrothermal breccia body (Fig. 3.7D). Potassic 2d: Late main stage potassic 2d occurs in the shallow eastern portion of the CRZ, where it is spatially associated with megacrystic orthoclase-phyric monzonites that crosscut the hydrothermal breccia body. Late stage alteration Calcic 4b, sericite-anhydrite-carbonate, and propylitic:  Late stage alteration  assemblages in the CRZ exhibit the same characteristics as in the NGL. They are best represented in the eastern part, which represents the shallower levels of the system; however, they are present throughout the CRZ where the minerals overprint older alteration stages (Figs. 3.11D and 3.11E). Sulfide mineral zonation A wedge-shaped Cu-enriched high-grade ore zone about 300m in width and 400-450m in length defines the CRZ (Figs. 3.9B and 3.11F). The high-grade zone forms a westerly inclined wedge that parallels the 45-60º west-southwesterly dipping syenite intrusions and the inferred hydrothermal breccia body. A poorly developed sulfide zonation characterizes the ore zone. Chalcopyrite with accessory bornite forms restricted, high-grade centers dominantly located near the upper eastern section of the ore zone. The higher Cu-grade zones are surrounded by a chalcopyrite-dominated shell, which extends toward the CRZ core. Chalcopyrite and pyrite are the dominant sulfides outward, and a gradual transition occurs into a sulfide-poor peripheral zone. A pyrite shell, as mapped at the NGL, is not evident, but may reflect the limited drill core coverage. As in the NGL, sulfide deposition in the CRZ occurred in two stages, which combined to form the ore shell (Figs. 3.9B and 3.11F). Early disseminated chalcopyrite and subordinate bornite accompanied potassic alteration 2a. This event contributed Cu and Au to the shallow 90  eastern part of the CRZ. The hydrothermal breccia body cut the early Cu and Au-rich shell. Chalcopyrite and pyrite precipitated in the second stage are concentrated on the central and eastern margin of the breccia body and form the lower, western extension of the composite ore shell. Overall, this second event is spatially subordinate to the earlier event, yet it introduced most of the Cu into the CRZ. Overall, the Cu (%): Au (g/t) ratio to 5:1, different from the 2:1 ratio characteristic of the NGL and SGL. 3.5.3  Hydrothermal paragenesis of the South Gold Lens (SGL)  The SGL was affected by most of the early and main stage alteration events mapped in the NGL and CRZ; however, the SGL has additional intrusive, brecciation, alteration and mineralization stages that complicate the section, resulting in a somewhat different unique hydrothermal alteration profile. Furthermore, the SGL is underlain at depth by the Bountiful Zone (Schwab et al., 2008), which is another Cu-rich prospect not investigated herein (Fig. 3.5). Because of the spatial association, however, there is some overlap of alteration and mineralization assemblages, between the deeper parts of the SGL and the underlying Bountiful Zone. Early and main stage alteration Potassic 1 and 2a and calcic 2b: Early potassic 1 and 2a stage alteration is best preserved in felsic volcanic rocks located in the upper central and eastern portions of the SGL (Figs. 3.6C and 3.6D). It is limited by the hydrothermal breccia body in the west and a large ~120m wide, sheeted megacrystic orthoclase-phyric monzonite dike complex in the center (Figs. 3.8A to 3.8C, 3.9A, and 3.12A to 3.12C). The sequence of potassic events 1 and 2a and calcic 2b, associated alteration assemblages, and crosscutting relationships are the same as for the NGL and CRZ. Alteration stages 2c and 2d are not known in the SGL.  91  92  Figure 3.12: Distribution maps of the five alteration types and associated assemblages in the South Gold Lens along section 6334100 (Fig. 3.2A). Only the dominant minerals are shown. Geology in Fig. 3.4A are shown as gray lines for reference. A) Potassic, calcic and propylitic alteration assemblages and sulfide distribution; B) orthoclase and specular hematite distribution; C) biotite and magnetite distribution; D) calcic alteration; E) Sodic, SAC and propylitic alteration assemblages; and F) metal zonation based on the distribution of copper (>0.5-1.5% Cu) and gold (>1.0-2.0 g/t Au). Evidence for the deeper Bountiful Zone is present in the deeper eastern parts of the section.  93  Potassic 3a: A weak, but pervasive potassic alteration assemblage is evident in close spatial association with megacrystic orthoclase-phyric monzonites and the orthoclase-phyric monzonites (Figs. 3.6F, 3.6H and 3.7H). White to lightly grey to rarely pink colored orthoclase, fine-grained shreddy biotite, and magnetite form the alteration assemblage. Disseminated chalcopyrite and pyrite are rare. The alteration stage is similar to potassic alteration stage 2d (Figs. 3.7G and 3.7L) in the NGL and CRZ. In the SGL, a pseudo-breccia texture characterizes potassic 3a. The apparent breccia texture forms where a dense network of fractures filled by orthoclase and with texture-destructive K-feldspar selvages cuts the rock. Calcic and potassic events 3b: A third stage of calcic and potassic alteration is intrinsically associated with, and restricted to, a polymictic magnetite-biotite-pyroxene cemented breccia body in the west part of the SGL (Figs. 3.7H and 3.11E). The breccia cuts all rocks and associated alteration assemblages. The calcic 3b assemblage is older than the closely related potassic 3b assemblage. The calcic 3b assemblage consists of abundant, coarse crystalline pyroxene (0.5 to 1cm) that has replaced clast margins and infilled cavities and fractures (Fig. 3.7H). Diopsidic pyroxene is compositionally zoned. The superposed potassic 3b assemblage consists of coarse crystalline biotite (0.5 to 0.8cm) and abundant magnetite with minor orthoclase (Fig. 3.7I) that has mantled and locally replaced diopsidic pyroxene. Potassic alteration stage 3b is also associated with minor sulfide mineralization. Massive bornite and chalcopyrite commonly occur as a separate cement phase with anhydrite, but has also infilled cavities within the hydrothermal breccia body. Large crystal sizes and distinctive zoning characterize the calcic and potassic alteration assemblages. Biotite also occurs as a dark, brown core surrounded by a green rim. Potassic event 3c: Sparsely distributed in the west and center of the SGL, the youngest potassic 3c stage occurs as distinct veins that crosscut all rocks, the breccia body, and associated  94  alteration assemblages (Fig. 3.7J). Their textural appearance and orientation is similar to the veins of potassic alteration stage 2c in the NGL. Late stage alteration Sodic: Albite, confined to within 50m of the South Fault (Fig. 3.12E), has pervasively replaced and destroyed all primary textures in the host rock (Fig. 3.7K). Chalcopyrite and bornite form large clusters within the shallow central portion of the sodic altered area; however, it is unclear whether the sulfides were introduced during potassic 2a and recrystallized, or, whether the sodic alteration event added new sulfide to the system. Albite replaced felsic host rocks and syenites, and also cross cuts the deeper section of the hydrothermal breccia body. A common characteristic of sodic alteration in the SGL is the bright white to pale grey color of albite, which is easily distinguishable from the pale cream to pink color of hydrothermal orthoclase. Calcic 4b: Weakly developed calcic alteration overprints the hydrothermal breccia in the west of the SGL (Fig. 3.12D). It shares the same textural and mineralogical characteristics as other calcic 4b alteration stages observed elsewhere, but is younger based upon cross cutting relations. Sericite-anhydrite-carbonate: As with the other centers, late SAC alteration is localized throughout the shallow portion of the SGL in the direct vicinity of the South Fault (Figs. 3.8D and 3.12E). Calcite is ubiquitous, whereas sericite is more localized and is closely associated with the megacrystic orthoclase-phyric monzonites and orthoclase-phyric monzonites (Fig. 3.7M). Propylitic: Late propylitic alteration forms localized zones in the west and center of the SGL (Figs. 3.8D, 3.9A, and 3.12E). Chlorite is prominent in areas that contain or were altered by biotite and hornblende. Epidote is minor and appears restricted to monzonites and the westerly located, hydrothermal breccia, where it replaces plagioclase and garnet. Siderite and ankerite 95  form part of the propylitic alteration assemblage. Both minerals typically form vein assemblages that dominate the western portion of the SGL. Veins are irregularly distributed. They range between 0.5 and 1.5 cm in thickness. Pyrite is scarce and disseminated or forms thin veins dominantly in the eastern portion of the SGL. Sulfide mineral zonation The SGL core is dominated by a Cu-Au enriched zone, which extends to the west, across the South Fault. It is up to 300m wide and about 300m long (Figs. 3.9B and 3.12A). A 45 to 60º southwest dipping, orthoclase-phyric sheeted monzonite dike complex bounds the ore zone on the east. The overall ore body geometry is wedge-shaped, with a westerly inclination similar to the NGL and CRZ. The high-grade core of the SGL is dominated by bornite + chalcopyrite, and is localized east of the South Fault (Fig. 3.9A). A chalcopyrite shell surrounds the core and extends west across the South Fault. Towards the east, a chalcopyrite - pyrite shell grades into a pyrite dominated peripheral zone. Towards the west, the chalcopyrite shell is crosscut by a younger chalcopyrite + bornite assemblage associated with a hydrothermal breccia. Thus, as in the NGL and the CRZ, the high-grade zone of the SGL is composite, interpreted to have formed as a result of two mineralization events. The older event introduced the bulk of copper and gold to the SGL. The overall Cu (%): Au (g/t) ratio is 2:1, comparable with the NGL. 3.5.4  Summary of the hydrothermal paragenesis  Five hydrothermal alteration assemblages overprint the host supracrustal rocks and some of the intrusive rocks. Crosscutting relationships, textural characteristics and relationship to intrusive units establish a paragenetic sequence regardless of absolute age that is divided into an early, main, and late stage, each with several distinguishable substages (Fig. 3.7). The  96  distribution and intensity of the alteration and sulfide mineral assemblages varies between the mineralized centers.  97  98  Figure 3.13: Paragenetic summary of hydrothermal alteration and mineralization events within the three mineralized centers of the Central Zone. Note that the timing and intensity of events varies between the three centers.  99  3.5.5  Age of Hydrothermal Alteration  Titanite is a common mineral of the hydrothermal alteration assemblage in the NGL and SGL, and was dated using the Sensitive High-Resolution IonMicroprobe (SHRIMP-RG; see Table A2.1 for analytical procedures). Coarse hydrothermal titanite intergrown with diopsidic pyroxene and anhydrite of calcic 2b stage from the SGL (GC0495-227.46m; Fig. 3.13A) was analyzed in situ in a polished thin section whereas hydrothermal titanite of potassic 2c stage in the NGL (GC0734-350.50m; Fig. 3.13B) was analyzed as a mineral separate. As titanite can commonly contain significant common Pb, the calculated  207  Pb/235U and  207  Pb/206Pb ages are  subject to a significant common Pb correction and hence uncertainty, as is evident from the U-Pb analytical data (Table A2.1). Hence, a weighted mean  207  Pb corrected  206  Pb/238U age better  approximates the age of the titanite (Ireland and Williams, 2003).  Figure 3.14: Hydrothermal titanite samples for U-Pb SHRIMP-RG analysis. A) South Gold Lens: coarse hydrothermal titanite intergrown with diopsidic pyroxene and anhydrite of calcic 2b stage (GC0495-227.46m) B) North Gold Lens: hydrothermal titanite of potassic 2c stage (GC0734-350.50m) derived from a coarse, pegmatitic orthoclase, biotite and titanite bearing vein (Fig. 3.7E).  100  In situ analysis using the SHRIMP-RG of three crystals of centimeter-sized titanite from the SGL demonstrates the effect of common Pb on the calculated age (Fig. 3.14A; Table A2.1). Regression of six of the ten spots suggests a crystallization age of 211.1±1.6 Ma, which agrees with the weighted mean  206  Pb/238U age of 210.8±2.4 Ma. Four spots have very different U-Pb  isotopic compositions, and there is no correlation between spot, U content, or % common Pb and 206  Pb/238U age. An explanation for the dispersion is unknown.  101  102  Figure 3.15: U-Pb Tera-Wasserburg concordia diagrams and weighted mean histograms for titanites from the CZ, Galore Creek, British Columbia. A) South Gold Lens; B) NGL; grey boxes in histogram are from the non-magnetic titanite whereas black boxes are for magnetic titanite.  103  Twenty-four titanite grains from two different magnetic fractions of the NGL have a considerable range of U-Pb ages (Fig. 3.14B; Table A2.1). A weighted mean age of  206  Pb/238U  ages for all 24 grains is 197.3±4.2 (MSWD=1.19), which is a statistically a valid age. What is of interest is that the weighted mean 206Pb/238U age for the different magnetic fractions statistically do not overlap, reflecting significant scatter in the data. Taking just the older grains and excluding grains with 206Pb/238U ages <190 Ma, a weighted mean 206Pb/238U age of 206±2.2 Ma (n=17) can be interpreted. This age is consistent with the field relations (see below).  3.6 Discussion 3.6.1  Tilting of the hydrothermal system  A hydrothermal model for the CZ deposit requires the integration of the geological architecture and a history of the three mineralized centers. Assessing any post-mineral history that might affect the geometry of the centers is of particular importance. The zonation of hydrothermal alteration and sulfide mineral distribution indicate an inclination of 45°-60º; westerly in the NGL and southwesterly in the CRZ and SGL. The spatial distribution and orientation of rocks in the east-west cross sections suggests that the hydrothermal system is subparallel to the dip of the host stratigraphy and subparallel to dike and intrusive contacts. However, surface geologic maps show that stratigraphy and intrusions are not subparallel, and that the megacrystic orthoclase-phyric monzonite intruded across bedding and stratigraphic units (Figs. 3.2A and 3.5). Apophyses emanate from the larger pluton along the stratigraphy (Fig. 3.2A) which makes them appear like sills on each other E-W cross-sections. Regardless, the field relations suggest that the host stratigraphy was tilted prior to intrusion of at least the megacrystic orthoclase-phyric monzonite, and presumably prior to the older orthoclase- and pseudoleucite-phyric syenites. 104  Porphyry Cu deposits and hydrothermal breccias generally form with a subvertical axis (e.g. Gustafson and Hunt, 1975; Seedorff et al., 2005). At Galore Creek, the inclined mineralized zones indicate significant post-mineral deformation. Moreover, the inclination for the three mineralized centers is different, with the NGL dipping 45° to 60º westerly, and the CRZ and SGL dipping 45° to 60º to the southwest. The different inclinations argue that the axis of rotation is not simply parallel to the ore bodies or the stratigraphy, but must have been somewhat oblique. A similar magnitude of post-mineral tilting and sense of inclination is proposed for the nearby Southwest zone (Byrne, 2009). The timing of tilting of orebodies is uncertain, but may be associated with the post-mineral, brittle thrust faults, which locally cut but also surround the mineralized zones. Logan and Koyanagi (1994; Logan, 2005) described four deformation events within the Stikine‐Iskut River region (Fig. 3.1B), three of which are recognized within the Galore Creek valley (Schwab et al., 2008). Deformation must explain pre-mineral tilt and folding of the supracrustal rocks prior to intrusion of the Late Triassic syenite and monzonite complex. Shortening during the late Triassic collapse of the marine arc and onset of amalgamation of the offshore island arc to North America (Nelson and Colpron, 2007; Colpron et al., 2007) probably accounts for that deformation. Post-mineral tilting of the Galore Creek district may reflect early Jurassic east‐west shortening accompanied by thrust faults, which would also have tectonically buried the porphyry Cu-Au district (Logan and Koyanagi, 1989a-b, 1994; Schwab et al., 2008), thereby preserving the deposit from erosion. 3.6.2  Timing of hydrothermal alteration  The 211±1.6 Ma shrimp U/Pb age for hydrothermal titanite in the SGL is consistent with the igneous titanite U-Pb age of 210±1 Ma for the host orthoclase and pseudoleucite-phyric syenite (Mortensen et al., 1995). The agreement in ages suggests that the causative linkage 105  inferred between these rocks and the hydrothermal system is valid (Enns et al., 1995). In the SGL, late main stage potassic 3 is associated with, and post-dates, the 205-Ma, megacrystic orthoclase-phyric monzonites. There are thus two superposed hydrothermal systems in the SGL, but the bulk of the Cu-Au formed early. The age of the bulk of the hydrothermal system in the NGL and superposed CRZ is open to interpretation. Early main stage alteration (potassic 2a) in the NGL predates and appears to be temporally associated with the orthoclase and pseudoleucite-phyric syenite, which are 210±1 Ma. However, the U-Pb ages for the hydrothermal titanite do not obviously support this age as the calculated  206  Pb/238U age for all titanite grains of 197.3±4.2 Ma conflicts with the cross  cutting relationship, as it is younger than the largely post-mineral megacrystic orthoclase and plagioclase-phyric monzonite of 205.1±2.3 Ma (Mortensen et al., 1995). The oldest possible 206  Pb/238U age of 206±2.2 Ma for hydrothermal titanite from the potassic 2c is consistent with  geologic relations, in that the megacrystic monzonite largely intruded the mineralized system but is also weakly altered in late main stage potassic 2d alteration. This age must be a minimum, as the genetic relationship between potassic 2c stage and either the syenite or monzonite is unknown. The 206±2.2 Ma age may reflect thermal disturbance of the ~210 Ma system by the megacrystic monzonite or reflect precipitation prior to intrusion of the large monzonite body. The geologic and geochronologic data confirm the presence of a second age of hydrothermal activity in the CZ. What is unknown is whether or not the bulk of the metalliferous hydrothermal fluids were derived from the ~210 Ma pseudoleucite-phyric syenite or the ~205 Ma megacrystic monzonite complexes, or both. Nonetheless, the geologic relations suggest at least two stages of mineralization compose the CZ. Taken together with the evidence of a still younger hydrothermal event precipitating Cu and Au elsewhere in the Galore Creek district (Schwab et al., 2008; Byrne, 2009), it seems reasonable to suspect that a series of temporally  106  distinct but largely similar intrusion-related hydrothermal events together form the Galore Creek district. 3.6.3  Hydrothermal evolution  Widespread potassic alteration is related to the bulk of the Cu and Au in the CZ (Allen et al., 1976; Enns et al., 1995; this study). In plan view, potassic alteration forms a northeastelongated footprint that envelopes the three mineralized centers composing the CZ as well as the calcic alteration zones (Fig. 3.2B). The most intense potassic alteration spatially coincides with highest metal grades (Fig. 3.9), where gold- and bornite-rich cores to the NGL and SGL are surrounded by a halo of chalcopyrite, with pyrite forming a distal fringe. Overall intense potassic alteration and high Cu-Au grade centers parallel and overlap the now-inclined intrusions. This spatial association suggests a genetic link between porphyry intrusions and the hydrothermal system, common to porphyry deposits around the world (Seedorf et al., 2005). U-Pb ages on hydrothermal titanite reported herein are consistent with the genetic association. Potassic alteration is intrinsically associated with hot (350°-550ºC), hydrothermal fluids characterized by high aK+/aH+ exsolved from intruding porphyry stocks and underlying plutonic complex (Beane and Titley, 1981; Dilles et al., 2000; Ulrich et al., 2001; Seedorf et al., 2005). In the case of the CZ, the alkalic silica-undersaturated syenites and monzonites are inferred to be the source of fluids, although the genetic ties to any of the main complexes is not unequivocal largely due to the complexity of the CZ and lack of geologic features that typically provide time-markers in the porphyry environment. Nonetheless, within the potassic alteration encompassing the CZ at Galore Creek, the distribution and general abundances of minerals was clearly controlled by several parameters common in porphyry Cu deposits (Beane and Titley, 1981), including the ferromagnesian mineral content in host rocks and the oxidation state of wall rocks and fluid. 107  Potassic fluids in the CZ were likely alkaline and oxidized based on their precipitants such as abundant anhydrite, specular hematite, and magnetite. The latter Fe-oxide minerals imply an abundance of ferric over ferrous iron in the hydrothermal fluid. Moreover, hematitestaining, or ‘reddening’, of secondary orthoclase is readily visible in feldspar-dominated rocks throughout the CZ. Wall rock reddening results from the oxidation of ferrous iron by hydrothermal fluids, leading to sub-micron sized hematite inclusions in secondary K-feldspar (Wilson et al., 2003). In the CZ, wall rock reddening is most evident in the monzonite and syenite intrusions and the felsic volcanic rock units; it is not evident in the more reduced environment of the mafic-rich rocks that lack significant amounts of K-feldspar alteration. Copper and gold coincide in part with the distribution of reddened rock units. Bornite introduced by early main stage potassic alteration may have preferentially replaced specular hematite. The correlation between bornite abundance and gold concentration in the NGL and SGL is common in the cores of many porphyry Cu deposits (Gammons and Williams-Jones, 1997; Kesler et al., 2002; Wilson et al., 2003), as it reflects precipitation of auriferous Cu-Fe sulfides at high temperature. Bornite can contain one order of magnitude more gold than coexisting chalcopyrite (Kesler et al., 2002), but more Au is recovered from chalcopyritedominated portions of porphyry Cu deposits simply because of the greater abundance of the mineral (Sillitoe, 2000). High-grade Cu in the CZ is related to the abundance of chalcopyrite. Chalcopyrite dominates the halo immediately surrounding bornite-rich centers, and is most prominent in the shallow portion of the CRZ where it envelopes the hydrothermal breccia body and associated calcic alteration zone (Figs. 3.9 and 3.11). Chalcopyrite replaced hydrothermal biotite and magnetite that formed during earlier potassic alteration. Away from the hot, oxidized fluiddominated centers represented by the potassic alteration zones are lower temperature environments that reflect reduced or a less oxidized environment wherein the fO2 is controlled 108  by ferromagnesian minerals in the wall rocks. Here, the ferrous iron in minerals can reduce the highly oxidized potassic fluids, thereby adding iron to the fluid, leading to biotite and magnetite precipitation accompanied by chalcopyrite and pyrite. The northeast-elongated calcic alteration zone in plan view appears centered on the CRZ hydrothermal breccia body (Fig. 3.2B). It encompasses the deep portions of the entire CZ, but extends north and south incorporating the breccia bodies of the NGL and the Bountiful Zone. It parallels the westerly dip of the breccias, as well as the general orientation of the intrusive rocks. Garnet is within or proximal to the core of the CZ, whereas peripheral diopsidic pyroxene and magnetite envelop the north, center and south margins of the breccia bodies. This zonation suggests a genetic link between calcic alteration, hydrothermal brecciation, and porphyry intrusions. Furthermore, it is equivalent to zonal patterns in porphyry Cu skarn systems (Einaudi, 1982; Meinert, 1997). Garnet and pyroxene stability suggests 400° to 700ºC hydrothermal fluids, which has been confirmed by limited fluid inclusion data derived from Galore Creek garnets (Lang et al., 1993; Dunne et al., 1994). The inferred temperature range is essentially that inferred for potassic fluids (Ulrich et al., 2000; Seedorff et al., 2005). Like the potassic fluids, the calcic fluids were also highly oxidized, as evinced by observed zonation patterns in particular the high garnet/pyroxene ratios (Meinert et al., 2005). Garnet demonstrates the subtle variations in oxidation state. In the center of the calcic alteration zone, garnet is dominantly dark brown, whereas in the more marginal regions garnet is dominantly pale beige. The color variations are equivalent to changes in composition from Tirich andradite to ferric iron-rich andradite to grossular (Russell et al., 1999; chapter 5), and reflect the availability of ferric iron for substitution of aluminum within the oxidized core of the calcic alteration system. However unlike many porphyry-skarn systems (Meinert et al., 2005), calcic alteration in the CZ is not directly associated with Cu-bearing sulfides, but rather formed a physical and chemical trap for sulfide precipitation. Hydrothermal fluids associated with calcic 109  alteration appear genetically associated with several or one large breccia systems that were subsequently cemented by a calc-silicate assemblage. Brecciation created permeability and provided a physical trap for fluids at the breccia margins. The calcic mineral cement and the redox gradient from oxidized core to reduced rim in the breccia formed the chemical trap. Superimposed on the calcic alteration, particularly at the breccia margins, is a younger stage of potassic alteration dominated by biotite and magnetite, indicating that the circulating hydrothermal fluids returned to high aK+/aH+ dominated conditions. This generation of biotite and magnetite was subsequently replaced and mantled by chalcopyrite, pyrite, and very rare bornite. The change from calcic to potassic alteration could have been caused by the depletion of calcium in the fluid through garnet, pyroxene, and anhydrite precipitation (Beane and Titley, 1981). However, since no intergrowth textures between sulfide and potassic minerals with calcic alteration minerals are observed, I suggest that the potassic alteration and second stage of sulfide mineralization is caused by a potential fresh influx of mineralized potassic fluids exsolved from an intrusive source at depth, rather than from an evolving hydrothermal fluid (Fig. 3.16).  110  111  Figure 3.16: The geological and hydrothermal evolution of the CZ. Main stage (1): Formation of one or multiple potassic alteration cells and mineralization in the Central Zone with emphasis on the NGL and SGL. Emplacement of a hydrothermal breccia body in the CRZ. Hydrothermal cementation lead to widespread calc-potassic alteration and mineralization. Main stage (2): Monzonite intrusion followed by emplacement of a hydrothermal breccia body in the SGL and potentially the development of the South Faults. Hydrothermal cementation leads to widespread calc-potassic alteration and minor mineralization. Late stage: Intrusive activity and brecciation ceased in the CZ. Onset of the waning stage of the hydrothermal system and development of a sodic alteration assemblage in the SGL and a widespread propylitic, calcic alteration assemblage due to the mixing of unknown fluids with magmatic discharge.  112  Most late alteration assemblages are marginal to the CZ, enveloping the potassic and calcic alteration footprint and are therefore not well represented on the long section through the core of the deposit (Fig. 3.8). Nevertheless, late calcic alteration commonly parallels, and spatially overlaps, the monzonitic intrusions. Elsewhere, late albite overprints part of the Cubearing SGL. A couple of mechanisms are possible to explain the late influx of Ca and Na into the hydrothermal system. External Ca and Na carried by circulating thermally driven connate fluids entered the hydrothermal system, as is common in many porphyry Cu systems (Fig. 3.16; Dilles et al., 1995; Seedorff et al., 2008; Jago, 2008). Alternatively, Lang et al. (1995) suggests that the Na and Ca alteration reflects magmatic-derived hydrothermal alteration. Regardless of the mechanism, the presence of Na- and Ca- alteration late in the hydrothermal evolution is characteristic of alkalic porphyry Cu systems (Lang et al., 1995b). SAC alteration in the CZ is scarce and restricted to the eastern and what would have been the upper parts of the hydrothermal system (Figs. 3.8, 3.10, 3.11, and 3.12). Weakly developed SAC alteration is a common characteristic in the alkalic porphyry deposits of British Columbia (Lang et al., 1995a; Baker et al., 1999; Jago, 2008) and New South Wales (Wilson et al., 2003; Holliday and Cooke, 2007). The SAC alteration is broadly analogous to phyllic alteration in porphyry Cu-Mo systems, but with a variable component of carbonate that suggest the fluid is buffered to higher (K++Ca2++Na+)/H+ fluid compositions throughout the life of the alkalic porphyry systems (Titley and Beane, 1981; Lang et al., 1995a) presumably by water rock reactions. In the case of Galore Creek, much of the SAC alteration has been removed by erosion. Peripheral to the magmatic-derived hydrothermal plume, thermally-driven circulation of meteoric water alters the country rock to a propylitic assemblage (Fig. 3.16). The propylitic alteration enveloped and overprinted onto the potassic and calcic alteration footprint (Figs. 3.2B, 3.7M and 3.7N), indicates local mixing of meteoric fluids and magmatic fluids that occurred at 113  the interface between the rising magmatic-derived hydrothermal plume and the peripheral thermally driven hydrothermal system (Titley and Beane, 1981; Dilles et al., 2000; Seedorff et al., 2005). 3.6.4  The Central zone — An end-member alkalic porphyry Cu-Au deposit  Galore Creek, and in particular the CZ, is considered the end-member example of a silica-undersaturated alkalic porphyry Cu-Au deposit. This classification stems from the spatial and temporal association with alkalic quartz-deficient pseudoleucite-bearing syenite and orthoclase phyric monzonite (Leuck and Russell, 1994; Lang et al., 1995a). Furthermore, the dominance of andraditic garnet and diopsidic pyroxene in the core of the CRZ distinguishes Galore Creek from all other alkalic porphyry Cu-Au deposits regardless of igneous association. Many other alkalic porphyry systems have garnet and actinolite as an alteration phase in the inner and hotter portions of the propylitic assemblage, as well as actinolite locally in the core in association with the typical potassic mineral assemblages of hydrothermal orthoclase, biotite, and magnetite (Lang et al., 1995b; Wilson et al., 2003, 2006; Jago, 2008; Pass, 2010). However, none of the known alkalic porphyry Cu-Au systems are characterized by coarse garnet and pyroxene in the high-temperature core. Ti-rich andradite to grossular garnet and peripheral diopside at Galore Creek precipitated from a distinct hydrothermal fluid phase associated with the large polymictic breccia that forms the core of the CZ. The calcic fluid (calcic stage 2b) post-dates significant potassic alteration (potassic stage 2a) and associated bornite-chalcopyrite, but preceded a second stage of potassic alteration (potassic stage 2b) and less abundant Cu-Fe sulfides, dominantly chalcopyrite. The petrologic evidence suggests it is the influx of a distinct Ca-rich hydrothermal fluid that distinguishes Galore Creek from other alkalic porphyry Cu-Au deposits.  114  3.7 The hydrothermal model – a summary   The currently inclined geometry of the CZ reflects post-mineral deformation that tilted the localized, spatially overlapping alteration centers and hydrothermal breccia bodies in the NGL, SGL and CRZ (Fig. 3.16). The close association of hydrothermal alteration and brecciation with porphyritic monzonite and syenite intrusions suggests a genetic association. The alkaline, silica-undersaturated magmas introduced several pulses of silicaundersaturated, highly oxidized and mineralized fluids.    Early main stage potassic fluids were controlled by the temperature and oxidation state of the fluid as well as the ferromagnesian mineral content of the host rocks. Associated sulfide minerals formed ore shells that are characterized by gold-rich Cu-core (bornite-dominated) with an alteration assemblage of hematite dusted orthoclase and specular hematite that is indicative of hot, oxidizing conditions.  The core is surrounded by a halo of biotite,  magnetite, chalcopyrite and barren pyrite indicative of a progressively cooler, more reduced environment outward.   Main stage brecciation and subsequent calcic alteration is centered on the CRZ and parts of the NGL (Fig. 3.16). The association of the brecciation, calcic alteration and sulfide mineralization imply an origin as porphyry skarn and thus argue for a genetic link to porphyritic intrusions at depth. A second-stage potassic fluid was channeled along the fractured and highly permeable margins of the breccia bodies, precipitating a second sulfide stage that spatially overlapped in part with the earlier main sulfide stage.    In the SGL, additional potassic and calcic alteration events appear associated with the youngest monzonitic porphyry intrusions and another hydrothermal breccia body (Fig. 3.16). Overall, the paragenetic sequence during early main stage alteration is repeated successively throughout the lifetime of the CZ. 115    SAC alteration formed in the reconstructed higher level of the hydrothermal system, and along faults in the core of the CZ (Fig. 3.16). Pyrite is the main sulfide. The SAC assemblage is inferred to be broadly equivalent to the sericite (phyllic) alteration common to porphyry Cu deposits. The widespread abundance of carbonate and anhydrite suggest that the fluid never evolved to low pH, which generally characterizes the intermediate temperature alteration stages in most porphyry Cu systems (Gustafson and Hunt, 1975; Seedorff et al., 2005).    Propylitic alteration in the CZ is presumed to have developed in a classic sense due to the influx of convecting, volatile-rich fluids into the waning hydrothermal system.  116  3.8 References Aleinikoff, J.N., Wintsch, R.P., Tollo, R.P., Unruh, D.M., Fanning, C.M., and Schmitz, M.D., 2007, Ages and origin of rocks of the Killingworth Dome, south-central Connecticut: Implications for the tectonic evolution of southern New England. American Journal of Science, v. 307, p. 63-118. Allen, D.G., Panteleyev, A. and Armstrong, A.T., 1976. Porphyry copper deposits of the alkalic suite: Galore Creek, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 402-414. Baker, T., Ash, C.H., and Thompson, J.F.H., 1999, Geological setting and characteristics of Red Chris porphyry copper-gold deposits, northwestern British Columbia: Exploration and Mining Geology, v. 6, p. 297-316. Barr, D.A, Fox, P.E., Northcote, K.E. and Preto, V.A., 1976. The alkaline suite porphyry deposits; a summary, in Sutherland Brown, A., Porphyry deposits of the Canadian Cordillera: Canadian Institute of Mining and Metallurgy, Special volume 15, p. 359-367. Beane, R.E., and Titley, S.R., 1981, Porphyry copper deposits; Part II: Hydrothermal alteration and mineralization in Skinner, B.J., ed., Economic geology, 75th Anniversary Volume: El Paso, The Economic Geology Publishing Company, p. 235-269. Byrne, K., 2009. The Southwest Zone breccia-centered silica-undersaturated alkalic porphyry Cu-Au deposit, Galore Creek, B.C: Magmatic-hydrothermal evolution and zonation, and a hydrothermal biotite perspective. Vancouver, University of British Columbia, M.Sc. thesis, 170 p. Byrne, K., Tosdal, R.M., and Simpson, K.A., 2010, Coherent and clastic rocks in the Southwest Zone alkalic porphyry Cu-Au system, Galore Creek, Canada (NTS 104G): Geoscience BC Summary of Activities 2009, Geoscience BC, Report 2010-1, p. 87-104. Cherniak, D.J., 1993, Lead diffusion in titanite and preliminary results on the effects of radiation damage on Pb transport: Chemical Geology, v. 110, p. 177–194. Colpron, M., Nelson, J.L., and Murphy, D.C., 2007, Northern Cordilleran terranes and their interactions through time: GSA Today, v. 17, no. 4/5, p. 4-9. Cooke, D. R., Wilson, A. J., House, M. J., Wolfe, R. C., Walshe, J. L., Lickfold, V. and Crawford, A. J., 2007, Alkalic porphyry Au - Cu and associated mineral deposits of the Ordovician to Early Silurian Macquarie Arc, New South Wales: Australian Journal of Earth Sciences, v. 54:2, p. 445-463. Davies, A.G.S., Cooke, D.R., Gemmell, J.B., and Simpson, K.A., 2008b, Diatreme breccias at the Kelian gold mine, Kalimantan, Indonesia: precursors to epithermal gold mineralisation: Economic Geology, v. 103, p. 717-757. Dilles, J.H., Farmer, G.L., and Field, C.W., 1995, Sodium-calcium alteration by non-magmatic saline fluids in porphyry copper deposits: Results from Yerington, Nevada: 117  Mineralogical Association of Canada Short Course, v. 23, p. 309-338. Dilles, J.H., Einaudi, M.T., Proffett, J.M., and Barton, M.D., 2000, Overview of the Yerington porphyry copper district: Magmatic to non-magmatic sources of hydrothermal fluids: Their flow paths and alteration affects on rocks and Cu-Mo-Fe-Au ores: Society of Economic Geologists Guidebook 32, p. 55-66. Dunne, K.P.E., Lang, J.R., and Thompson, J.F.H., 1994, Fluid inclusion studies of zoned hydrothermal garnet at the Galore Creek Cu-Au porphyry deposit, northwestern British Columbia: Geological Association of Canada-Mineralogical Association of Canada, Program with Abstracts v. 19, p. A31. Einaudi, M.T., 1982, General features and origin of skarns associated with porphyry copper plutons, southwestern North America, in Titley, S.R., ed., Advances in Geology of the Porphyry Copper Deposits, Southwestern U.S.: Tucson, University of Arizona Press, p.185-209. Enns S.G., Thompson, J.F.H., Stanley, C.R. and Yarrow, E.W., 1995. The Galore Creek porphyry copper-gold deposits, northwestern British Columbia in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordillera of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 640-644. Frost, B.R., Chamberlain, K.R., and Schumacher, J.C., 2000, Sphene (titanite): phase relations and role as a geochronometer: Chemical Geology, v. 172, p. 131–148. Gammons, C.H., and Williams-Jones, A.E., 1997, Chemical mobility of gold in the porphyryepithermal environment: Economic Geology, v. 92, p. 45–59. Gustafson, L.B., and Hunt, J.P., 1975, The porphyry deposit at El Salvador, Chile: Economic Geology, v. 70, p. 857-912. Holiday, J.R. and Cooke, D.R., 2007, Advances in geological models and exploration methods for copper ± gold porphyry deposits, in Ore Deposits and Exploration Geology, Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration, p.791-809. Ireland, T.R., and Williams, I.S., 2003, Consideration in zircon geochronology by SIMS, in Hanchar, J.M., and Hoskin, P.W.O., eds., Zircon: Reviews in Mineralogy and Geochemistry, v. 53, p. 215-241. Jago, P., 2008, Metal- and alteration-zoning, and geochemical dispersion halos in the context of Cu-Au mineralization at the silica-saturated Mt. Milligan alkalic porphyry deposit: Unpublished Master’s thesis, University of British Columbia, p.210. Jensen, E.P., and Barton, M.D., 2000, Gold deposits related to alkaline magmatism: Reviews in Economic Geology, v. 13, p. 279-314. Kesler, S.E., and Chryssoulis, S.L, and Simon, G., 2002, Gold in porphyry copper deposits: its abundance and fate: Ore Geology Reviews, v. 21, p. 103-124. 118  Lang, J.R., 1994, Major and trace element compositional zoning in hydrothermal and igneous garnets from alkalic intrusive complexes In British Columbia: Geological Society of America Program with Abstracts, v. 26, p. A-369. Lang, J.R., Thompson, J.F.H., and Dunne, K.P.E., 1993, Hydrothermal garnet from the Galore Creek Cu-Au porphyry deposit, B.C. Canada: Implications of geochemical and fluid inclusion zoning patterns: Geological Society of America Abstracts with Program, v. 25, p. A-402. Lang, J.R., Lueck, B., Mortensen, J.K., Russell, J.K., Stanley, C.R. and Thompson, J.F.H., 1995a, Triassic-Jurassic silica-undersaturated and silica-saturated alkalic intrusions in the Cordillera of British Columbia: Implications for arc magmatism: Geology, v. 23, p. 451454. Lang, J.R., Stanley, C.R., Thompson, J.F.H., and Dunne, K.P.E., 1995b, Na-K-Ca magmatic hydrothermal alteration in alkalic porphyry Copper gold deposits, British Columbia, in Thompson, J.F.H., ed., Magmas, Fluids, and Ore Deposits: Mineralogical Association of Canada, v. 23, p. 339-366. Logan, J.M., 2005, Alkaline magmatism and porphyry Cu-Au deposits at Galore Creek, northwestern British Columbia: B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2004, Paper 2005-1, p. 237-248. Logan, J.M., and Koyanagi, V.M., 1989 a. Preliminary Geology and Mineral Deposits of the Galore Creek Area, North-western British Columbia (104G/7W): B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1989-1, p. 269-284. Logan, J.M., and Koyanagi, V.M., and Rhys, D.A., 1989b, Geology and mineral occurrences of the Galore Creek Area (104A and B): B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1989-8. Logan, J.M., and Koyanagi, V.M., 1994, Geology and mineral deposits of the Galore Creek area, northwestern British Columbia (104G/3 and 4): BC Ministry of Energy, Mines, and Petroleum Resources, Bulletin 92, 96 p. Lowell, J.D. and Gilbert, J.M., 1970, Lateral and vertical alteration-mineralization zoning in porphyry ore deposits: Economic Geology, v. 65, p. 373-408. Lueck, B.A. and Russell, J.K., 1994. Silica-undersaturated, zoned, alkaline intrusions within the British Columbia Cordillera: B.C. Ministry of Energy, Mines and Petroleum Resources, Report: 1994-1, p. 311-315. Ludwig, K.R., 2001, Squid (1.13b), A users manual, Berkeley Geochronology Center Special Publication No. 2, 15 p. Ludwig, K.R., 2008, Isoplot (3.6), A geochronological toolkit for Excel, Berkeley Geochronology Center Special Publication No. 4, p.78. 119  Mazdab, F.K., 2009, Characterization of flux-grown trace-element-doped titanite using the highmass-resolution ion microprobe (SHRIMP-RG): Canadian Mineralogist, 47, p. 813-831. Meinert, L.D., 1997. Application of skarn deposit zonation models to mineral exploration: Exploration and Mining Geology, v.6, p.185-208. Meinert, L.D., Dipple, G.M. and Nicolescu, S., 2005. World skarn deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R., and Richards, J.P., eds., Economic Geology, One hundredth anniversary volume: Littleton, Society of Economic Geologists, p. 299-336. Micko, J., Tosdal, R.M., Dipple, G., Barker, S., and Kent, A., 2009, Calcic alteration and hydrothermal brecciation in the Central Zone deposit, Galore Creek alkalic Cu-Au porphyry district, B.C., Canada: Society for Geology Applied to Mineral Deposits, Proceedings 10th Biennial Meeting, p. 278-280. Micko, J., 2010. The geology, genesis, and exploration context of the Central Zone alkalic CuAu porphyry deposit, Galore Creek district, northwestern British Columbia, Canada. Vancouver, University of British Columbia, unpublished Ph.D. thesis. Mihalynuk, M.G., Nelson, J., and Diakow, L.J., 1994, Cache Creek Terrane entrapment; oroclinal paradox within the Canadian Cordillera: Tectonics, v. 13, p. 575-595. Monger, J.W.H., 1977. Upper Palaeozoic rocks of the western Canadian Cordillera and their bearing on Cordilleran evolution: Canadian Journal of Earth Sciences, v. 14, p. 18321859. Monger, J.W.H, Wheeler, J.O, Tipper, H.W., 1992. Upper Devonian to Middle Jurassic assemblages: Cordilleran terranes (modified): Geological Society of America, G-2, p. 281-317. Mortensen, J.K., Ghosh, D. and Ferri, F., 1995. U-Pb age constraints of intrusive rocks associated with copper-gold porphyry deposits in the Canadian Cordillera, in Schroeter, T.G., ed., Porphyry deposits of the Northwestern Cordilla of North America: Canadian Institute of Mining, Metallugy, and Petroleum Special Volume 46, p. 142-158. Mortimer, N., 1987. Late Triassic and Early Jurassic subduction-related volcanism in British Columbia. Canadian Journal of Earth Sciences, v. 24, p. 2521-2536. Nelson, J. and Colpron, M., 2007. Tectonics and metallogeny of the British Columbia, Yukon and Alaskan Cordillera, 1.8 Ga to present, in Goodfellow, W. D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Special Publication 5, Mineral Deposits Division, Geological Association of Canada, p.755-791. NovaGold Resources Inc., 2008. NovaGold Expands Galore Creek Resource Estimate. Press release, URL<http://www.novagold.com/upload/pdf/NGReserve_ResourceTable.pdf> [June, 2008].  120  Pass, H., 2010, Breccia-hosted chemical and mineralogical zonation patterns of the Northeast Zone, Mt. Polley Cu-Ag-Au alkalic porphyry deposit, British Columbia, Canada: Unpublished Ph.D. thesis, University of Tasmania, Australia, p.240. Russell, J., Dipple, G.M., Lang, J.R. and Lueck, B., 1999. Major-element discrimination of titanium andradite from magmatic and hydrothermal environments; an example from the Canadian Cordillera: European Journal of Mineralogy, v.11, p. 915-935. Schwab, D. L, Petsel, S., Otto, B. R., Morris, S. K., Workman, E. and Tosdal, R. M., 2008, Overview of the Late Triassic Galore Creek Copper-Gold-Silver Porphyry System, in Spencer, J.W., and Titley, S.R., eds., Ores and orogenesis: Circum-Pacific tectonics, geologic evolution and ore deposits: Tucson, Arizona Geological Society Digest 22, p. 471-484. Schoene, B., and Bowring, S.A., 2007, Determining accurate temperature-time paths from U-Pb thermochronology: An example from the Kaapvaal craton, southern Africa: Geochimica et Cosmochimica Acta, v. 71, p. 165-185. Scott, J.E., Richards, J.P., Heaman, L.M., Creaser, R.A., and Salazar, G.S., 2008, The Schaft Creek porphyry Cu-Mo (-Au) deposit, northwestern British Columbia: Exploration and Mining Geology, v. 17, p. 163-196. Seedorff, E., Dilles, J. H., Proffett, J. M., Einaudi, M. T., Zurcher, L., Stavast, W. J. A., Johnson, D. A., and Barton, M. D., 2005, Porphyry Deposits: Characteristics and Origin of Hypogene Features: Economic Geology, 100th Anniversary Volume, p. 251-298. Seedorff, E., Barton, M.D., Stavast, W.J.A., and Maher, D.J., 2008, Root zones of porphyry systems: Extending the porphyry model to depth: Economic Geology, v. 103, p. 939956. Sillitoe, R.H., 2000, Gold-rich porphyry deposits: Descriptive and genetic models and their role in exploration and discovery: Reviews in Economic Geology, v. 13, p. 315-345. Sillitoe, R.H., 2010, Porphyry copper systems: Economic Geology, v. 105, p. 3-41. Titley, S.R. and Beane, R.E., 1981, Porphyry copper deposits, Part I: Geological settings, petrology, tectogenesis, in Skinner, B.J., ed., Economic geology, 75th Anniversary Volume: El Paso, The Economic Geology Publishing Company, p. 214-269. Titley, S.R., 1982, The style and progress of mineralization and alteration in porphyry copper systems: American Southwest, in Titley, S.R., ed., Advances in geology of the porphyry copper deposits, southwestern North America: Tuscon, Univeristy of Arizona Press, p. 93-116. Ulrich, T., Gunther, D., and Heinrich, C.A., 2001, The evolution of a porphyry Cu-Au deposit, based on LA-ICP-MS analysis of fluid inclusions of fluid inclusions: Bajo de la Alumbrera, Argentina: Economic Geology, v. 96, p. 1743-1774.  121  Williams, I.S., 1997, U-Th-Pb geochronology by ion microprobe: not just ages but histories: Society Economic Geologists Reviews in Economic Geology, v. 7, p. 1-35. Wilson, A. J., Cooke, D. R., and Harper, B., L., 2003, The Ridgeway gold–copper deposit: a high-grade alkalic porphyry deposit in the Lachlan Fold Belt, New South Wales, Australia: Economic geology, v. 98, p. 1637-1666. Wilson, A.J., Cooke, D.R., Harper, B.J., and Deyell, C.L., 2007. Sulfur isotopic zonation in the Cadia district, NSW: Exploration significance and implication for the genesis of alkalic porphyry gold-copper deposits: Mineralium Deposita, v. 42, no.5, p. 465-487.  122  4  Whole rock and isotope geochemistry of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada3  4.1 Introduction Exploration for porphyry Cu (-Au-Mo) deposits requires the recognition of their general alteration mineralogy, geochemical dispersion characteristics, and geophysical expression (Titley and Beane, 1981; Sillitoe, 2000 and 2010). These features, and their broad distribution in a mineralized porphyry intrusions, are reasonably well characterized (e.g. Jones, 1992; Garwin, 2002; Seedorff et al., 2005; Sillitoe, 2010), and reflect the interaction between magmatic-derived hydrothermal fluids, their wall rock, and thermally driven circulation of connate fluids (Dilles et al., 1987). Such water-rock interaction leaves a geochemical record that reflects these processes and fluid sources, leading to a geochemical footprint that extends beyond the known area of sulfide mineral deposition. Many investigations of the dispersion halos around porphyry Cu systems predate the modern geochemical and isotopic analytical techniques (e.g. Chaffee et al., 1971) that allow for determination of geochemical concentrations at levels below average crustal abundances. These new analytical advances permit the examination of the full geochemical effect of the hydrothermal system associated with porphyry Cu deposits and the full extent of geochemical dispersion halos. The alkalic-class of porphyry Cu-Au deposits provide a particular challenge, as the metal concentrations are typically associated with small volume, pipe-like intrusions that may have  3  A version of this chapter will be submitted for publication. Micko, J., Halley, S., Tosdal, R.M., and Bissig, T. (2010) Whole rock and isotope geochemistry of the Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada.  123  aerial extents of only a few hundred square metres (Jensen and Barton, 2000; Sillitoe, 2000; Wilson et al., 2002; Wilson et al., 2003). Supergene enrichment, and accompanying argillic alteration during weathering, is poorly developed due to the much lower pyrite contents of the hypogene alteration assemblages (Cooke et al., 2002). Furthermore, in northern areas such as British Columbia (Canada), recent glacial erosion commonly has removed the upper parts of most porphyry hydrothermal systems, thereby exposing the level of K-silicate alteration where the peripheral hypogene alteration commonly is the narrowest. Moreover, the alkalic porphyry Cu deposits are typically hosted in submarine mafic-dominated volcanic sequences that may have undergone pre-hydrothermal sea floor or burial metamorphism leading to a metamorphic mineral assemblage (chlorite-epidote) similar in character to the distal propylitic alteration that surrounds porphyry Cu deposits. Thus, methods must be devised to identify the distal and local hydrothermal alteration features associated with alkalic porphyry Cu-Au deposition. Alkalic-type Cu-Au porphyry systems are well represented in the upper Triassic to lower Jurassic Intermontane Belt of British Columbia, Canada (Barr et al., 1976; Lang et al., 1995a) and the upper Ordovician to lower Silurian Lachlan Fold Belt, New South Wales, Australia (Wilson et al., 2003; Cooke et al., 2007). The Galore Creek district, located in northwestern British Columbia about 100km northeast of Wrangell, Alaska (Fig. 4.1), arguably represents the end-member example of the silica-undersaturated class of alkalic porphyry Cu-Au deposits (Lang et al., 1995b). The district contains five explored prospects and six other mineralized centers with only limited exploration; its combined measured and indicated resources are estimated at 785.7 million tonnes grading at 0.52% Cu, 0.29g/t Au and 4.87g/t Ag (NovaGold Resources Inc., 2008). The district’s largest prospect is the Central Zone (CZ) that contains several adjacent and overlapping mineralized centers (Enns et al., 1995; Schwab et al., 2008; Micko et al., in review; chapter 3) and represents the focus of this study (Fig. 4.2).  124  Figure 4.1: A) Generalized distribution of the Stikine and Quesnel terranes in northwestern British Columbia showing the location of the Galore Creek Cu-Au porphyry district and other porphyry Cu centers. B) Regional geology of the northwestern Stikine terrane in the vicinity of Galore Creek. Modified after Logan and Koyanagi (1994).  125  Figure 4.2: A) Interpreted surface bedrock geology of the Central Zone showing the location of three E-oriented cross-sections that crosscut the principal mineralized centers, the North Gold Lens (NGL), Central Replacement Zone (CRZ), and the South Gold Lens (SGL), of which the NGL and CRZ are the foci for this study. The geology is modified after NovaGold Resources Inc. (2007). B) Surface alteration and sulfide mineral distribution of the Central Zone, modified from Schwab et al. (2008).  The hydrothermal alteration of wall rocks and porphyry intrusions leads to changes in major and trace element chemistry, as well as stable and radiogenic isotope composition, thus 126  producing hydrothermal anomalies of varying extent surrounding and overlying the deposit. The distribution of these features has long been recognized (Jerome, 1966; Jones, 1982; Chaffee, 1971; Garwin, 2002). In addition, district and deposit-scale investigations of variations in δ34Ssulfide/sulfate values suggest a distinct zoning may characterize some ore forming systems, particularly those in the alkalic porphyry environment (Halley et al., 2006; Neumayr et al., 2006; Walshe et al., 2006, Wilson et al., 2007) However, most studies do not correlate geochemical and isotopic zonations with the intensity or type of alteration assemblages, and many disregard individual stages of paragenetic evolution of the hydrothermal system (Mauk and Simpson, 2007). The geochemistry and S-isotopic composition of wall rock alteration at the Central Zone deposit, Galore Creek alkalic Cu-Au porphyry district are examined herein. Firstly, the multielement and isotope analytical methods applied in the characterization of lithological units, hydrothermal alteration assemblages, and zones of high-grade mineralization are documented. Secondly, the subtle and often cryptic alteration zones as well as geochemical dispersion halos highlighting proximity to a mineralized intrusive centre at known deposits are described. Finally, the combined techniques and their application to Galore Creek alkalic porphyry deposits are assessed.  4.2 Geological setting The Cordilleran tectonic collage of British Columbia contains the largest concentration of alkalic porphyry Cu-Au deposits and prospects in the world. The deposits and prospects are scattered over the 1500 km strike length of the Late Triassic and Early Jurassic magmatic arc that composes the inboard Quesnell and outboard Stikine terranes. The Galore Creek district, located at the northwestern margin of the Stikine terrane (Fig. 4.1A), is hosted within the lower Devonian to upper Permian Stikine assemblage and the lower to upper Triassic Stuhini Group. 127  The oldest rocks of the Stikine assemblage lying northeast of Galore Creek (Fig. 4.1B) are strongly deformed Devonian to Permian limestones, interbedded with mafic and intermediate lavas and volcaniclastic units, as well as a thin succession of middle Triassic siltstones, sandstones, and cherts (Monger, 1977; Enns et al., 1995; Logan, 2005). Unmetamorphosed rocks of the upper Triassic Stuhini group underlying the Galore Creek valley are subdivided into a lower unit of submarine basaltic to andesitic volcanic rocks interspersed with locally derived sandstones and siltstones (Allen et al., 1976) and an upper unit of partially subaerial, compositionally distinct alkali-enriched volcanic and volcanogenic sedimentary rocks (Micko et al., in review; chapter 3). The Stuhini Group rocks host the Late Triassic alkalic intrusive complex and the related hydrothermal systems. Sedimentary rocks equivalent to the lower Jurassic Hazelton Group that postdate mineralization are preserved north and east of Galore Creek, as are the lower Jurassic to lower Tertiary successor-basin sedimentary rocks of the Bowser Lake and Sustut Groups (Fig. 1B; Allen et al., 1976; Logan, 1989a, b; Enns et al., 1995). Steeply inclined (60° to 75º westerly) Eocene quartz monzonite and diorite stocks, as well as mafic to felsic dykes of unknown age, intrude the Triassic rocks throughout the Central Zone and exploit a west- and north-striking fault or fracture mesh (Enns et al., 1995).  4.3 Central Zone geology The CZ deposit consists of three mineralized and overlapping centers, the North Gold Lens (NGL), Central Replacement Zone (CRZ), and South Gold Lens (SGL). This study focused only on the NGL and CRZ, as the South Gold Lens lacks sufficient sample material preserved and is geologically complex due to multiple superposed hydrothermal systems and faults that juxtapose separate parts of the SGL (Enns et al, 1995; Micko et al., in review; chapter 3). 128  The mineralized centers of the NGL and CRZ are up to 350 to 500m wide, 400m to 700m deep (current exploration depth) and covered by 10 to 80m of Quaternary glacial deposits. The upper 10 to 100 m of bedrock is fragmented due to the hydration and dissolution of an anhydritefilled fracture-mesh.  The mineralized centers are tilted 45° to 60°northeast to east post  mineralization, thus the current outcrop preserves an oblique view of the porphyry systems. In this context, the upper preserved parts of the Galore Creek deposits lies on the east, whereas the deeper parts lie on the west (Micko et al., in review; chapter 3). With the exception of the SGL, the small displacement reverse faults that cut the district and mineralized ore shells do not greatly affect the distribution of mineralized rocks and the attending geochemical dispersion halos (Fig. 4.2A; Schwab et al., 2008; Byrne, 2009; Micko et al., in review; chapter 3). In plan view, the CZ displays an N-oriented, ellipsoidal alteration footprint that is about 2km in length and 1km in width (Fig. 4.2B). While the core of the system is dominated by a calc-potassic assemblage, the northern and southern centres are controlled by locally variable, potassic alteration. The margins of the CZ are commonly overprinted by peripheral calcic, propyllitic, and fine grained sericite (fine grained muscovite)-anhydrite-carbonate (SAC) alteration. The SAC, as well as localized sodic alteration, are commonly found in association with fault zones. Hydrothermal activity in the CZ is late Triassic in age based on the U-Pb ages on hydrothermal titanite of 211±1.6 Ma in the SGL and 206 ±2.2 Ma in the NGL (Micko et al., in review; chapter 3). Significant Au-Cu is associated with the emplacement of the syenite intrusions into the NGL. Subsequent less-extensive mineralization stages are affiliated with the calc-potassic alteration events and brecciation centered in the CRZ. Thus, the Cu:Au ratio for the NGL and SGL is 2:1 (>1g/t Au), whereas a 5:1 ratio (>0.3g/t Au) applies to the CRZ (Schwab et al., 2008).  129  4.3.1  North Gold Lens - geology  Rock units of the NGL strike west-northwest and dip 45° to 60º south-southwest (Table 4.1). They include fine-grained sandstone to siltstone and ribbon chert, overlain by sub-alkaline hornblende and plagioclase-phyric basaltic andesite, sub-alkaline to alkaline augite-phyric basaltic rocks, orthoclase-phyric trachyte, as well as pseudoleucite-phyric trachyte and derivative clastic rocks. Multiple fingering intrusions, generally displaying sub-parallel dips to the host sequence in cross section, cut the host rocks. These intrusions are grouped into an early-stage syenitic-dominated suite that includes pseudoleucite-phyric, orthoclase and pseudoleucitephyric, and orthoclase-phyric syenites, and younger megacrystic orthoclase and plagioclasephryic monozonites. Localized in the western margin is a pyroxene-biotite-magnetite-cemented, polymictic breccia that represents the lateral extension of the garnet-biotite-anhydrite breccia centred on the CRZ (Fig. 4.3A).  Table 4.1: Summary of the supracrustal host rocks and the CZ intrusive suite present in the NGL and CRZ section. Younger rock units such as Eocene intrusions are irrelevant to the hydrothermal system evolution and have been excluded from this summary. A detailed account of the lithologic units of the CZ can be found in thesis chapter 2. Lithologic unit Silt- to sandstone, and/or banded chert  Composition Matrix: Siltstone to fine grained sandstone; primary mineralogy unknown Texture: Locally planar to lightly folded laminae  Hornblende and plagioclasephyric basaltic andesite  Phenocrysts (bimodal): 0.1 to 0.3cm; 10 to 15%; evenly distributed, euhedral to subhedral orthoclase and hornblende  (coherent lavas and clastic units present)  Groundmass: medium to dark green, aphanitic Clasts: 1 to 8cm; > 35 to 50%, sparse orthoclase-phyric and granitic xenoliths (1 to 5cm) Matrix: fine grained, chlorite, biotite, felspars  Augite-phyric basalt  Phenocrysts: 0.1 to 0.7cm; 5 to 15%; evenly distributed, euhedral to subhedral augite  (coherent lavas and clastic units present)  Groundmass: dark green to black, aphanitic to finely crystalline; biotite, hornblende +/- pyroxene Clasts: 1 to 6cm; > 60%, augite-phyric clasts and sparse granitic xenoliths and lithic fragments (0.5 to 1cm) Matrix: Fine grained volcaniclastic material, contains augite crystal shards  130  Lithologic unit  Composition  Pseudoleucite-phyric trachyte  Phenocrysts: 0.3 to 1.2cm; 10 to 25%; trapezohedral, euhedral to subhedral pseudoleucite, rare bimodal phenocryst population with 0.1 to 0.3cm; 5 to 7%; tabular, subhedral orthoclase crystals.  (coherent lavas, intrusions and clastic units present)  Groundmass: light grey to pink (hem-dusted orthoclase), aphanitic, orthoclase ± nepheline ± pseudoleucite Occurs as small (80cm to 1.5m thick) intrusion (rare). Recognized more often as intrusive hyaloclastite (peperites) with distinctly fluidal margins (1 to 35cm). Facies range from fine sandstone to pebble conglomerate (or breccia)  Orthoclase-phyric trachyte  Phenocrysts: 0.3 to 1.2cm; 10 to 15%; intact, equant to tabular, irregularly distributed euhedral to anhedral orthoclase.  sub-volcanic intrusion  Groundmass: dark grey to black, aphanitic to fine grained, typically replaced by orthoclase and biotite.  Orthoclase and pseudoleucite-phyric syenite  Phenocrysts bimodal: (1) 0.5 to 1.2cm; 2 to 3%; subhedral, resorbed orthoclase; (2) 0.7 to 1.0cm; 1 to 2%; subhedral, resorbed pseudoleucite. Groundmass: light to dark grey, fine grained,orthoclase and biotite  Orthoclase-phyric syenite  Phenocrysts: 0.8 to 2cm, occasionally up to 3cm; sparse (3 to 5%); tabular, euhedral to subhedral orthoclase, locally resorbed.  (several sub-units present)  Groundmass: fine grained, dominated by orthoclase and small amounts of biotite, contains sparse mafic xenoliths (biotite and chlorite replaced, rounded) – unknown origin.  Megacrystic orthoclase and plagioclase-phyric monzonite  (1) Phenocrysts bimodal: (a) 1.2 to 2.5cm; 3 to 5%; equant to tabular, irregularly to trachytic, locally resorbed, orthoclase megacrysts; (b) 0.1 to 0.5cm; 5 to 7%; subhedral, plagioclase. Sub-unit (1) is the most common intrusive type in the NGL and CRZ.  Sub-units (1) and (2)  (2) Phenocrysts bimodal: (a) 1.5 to 4.5cm; 5 to 7%; tabular, euhedral, trachytic, oscillatory zoned orthoclase megacrysts; (b) 0.1 to 0.5cm; rounded, locally tabular, subhedral plagioclase. Plagioclase abundances vary (5 to 15%). Groundmass: light grey to green, coarse grained, composed of feldspar (60%), biotite (20%), hornblende (15%), and magnetite (5%).  Polymictic, diopside, biotite, and magnetite-cemented breccia (NGL)  Clasts: 1 to 80cm, max. 3m; volcanogenic sedimentary rock (50%), orthoclase and pseudoleucite-phyric syenite (25%), augite-phyric volcanic rocks (10%).  Polymictic, garnet, biotite, and anhydrite-cemented breccia (CRZ)  Clasts: 1 to 80cm, max. 2.5m; volcanogenic sedimentary rock (70%), orthoclase and pseudoleucite-phyric syenite (25%); fluidally-shaped, very fine-grained, black clasts of unknown origin (5%) ~juvenile clast?  Cement: 5 to 50%; fine crystalline aggregates and coarse crystals (0.5 to 2 cm) of diopside (30%), biotite (20%), magnetite (15%), garnet (10%), orthoclase (10%), and anhydrite (10%); chalcopyrite, pyrite and minor bornite (5%) infill void spaces with anhydrite and replace biotite and magnetite  Cement: 5 to 50%; fine crystalline aggregates and coarse crystals (0.5 to 3cm) of garnet (35%), biotite (20%), anhydrite (15%), diopside (10%), magnetite (5%), and orthoclase (5%); chalcopyrite and minor bornite (5%) infill void spaces with anhydrite and replace biotite and magnetite  131  Figure 4.3: A) Distribution of lithologic units in the NGL cross-section (6335550). B) Hydrothermal alteration assemblages and sulfide mineral distribution in the NGL cross-section.  Two mineralization phases formed an ellipsoidal ore shell, which in cross-section view is 350m in width and 500m in length and defines the core of the NGL (Fig. 4.3B). The mineralized core is characterized by Au-bearing bornite + chalcopyrite. Outwards, the sulfide assemblage 132  grades into a medial chalcopyrite domain, then into chalcopyrite + pyrite, and is surrounded by pyrite, which lacks Au. Late, post-mineral megacrystic orthoclase and plagioclase-phyric monzonites intrude the upper northwest corner of the mineralized shell. The high-grade bornite + chalcopyrite core is hosted by pseudoleucite-phyric trachyte and derivative clastic rocks and orthoclase (and pseudoleucite)-phyric syenites that are altered to a potassic assemblage of light grey to pink (hematite dusted), texturally destructive orthoclase, biotite magnetite, specular hematite, and anhydrite. Chalcopyrite has also replaced bornite. At the western margin of the NGL, the Au-enriched, bornite + chalcopyrite core extends into a hydrothermal breccia body (Fig. 4.3B), where high grade is dominantly confined to clasts derived from previously potassic altered rock units. Clasts are cemented by hydrothermal diopsidic pyroxene, biotite, magnetite, as well as lesser garnet (andradite to grossular), orthoclase and anhydrite, forming a calc-potassic alteration (Micko et al., in review; chapters 3 and 5). The alteration is roughly confined to the limits of the breccia body in the west of the NGL, but also extends into the underlying mafic rock units. A second stage of chalcopyrite, pyrite, and minor bornite form massive hydrothermal cement in the breccia and disseminated mineralization in the mafic volcanic rocks. The chalcopyrite halo is spatially associated with the shallowest portion of the pseudoleucite-phyric trachyte, and derivative clastic rocks, and orthoclase-phyric trachyte (Fig. 4.3B). Sulfide in the central section of the halo is associated with a potassic alteration assemblage. Sulfides emplaced during calc-potassic alteration form the lower and westernmost extension of the medial, Cu-enriched chalcopyrite halo. The chalcopyrite + pyrite halo is localized on the western and central section of the augite-phyric basalts (Fig. 4.3B) that are commonly replaced by the early main stage potassic assemblage of biotite, magnetite, minor orthoclase, and anhydrite. Disseminated chalcopyrite and pyrite replaced magnetite and biotite. 133  Late sericite-anhydrite-carbonate and propyllitic alteration introduced additional pyrite (Micko et al., in review; chapter 3) that formed disseminated cubes or vein fill, and overprints earlier potassic and calc-potassic assemblages in the eastern portion of the NGL. 4.3.2  Central Replacement Zone-geology  An andradite-biotite-anhydrite-cemented breccia is the dominant rock type exposed on the section investigated across the Central Replacement Zone (Table 4.1; Fig. 4.4A). Limited pseudoleucite-phyric trachyte and derivative clastic rocks are present on the eastern side of the cross-section. No other host sequence is preserved.  Figure 4.4: A) Distribution of lithologic units in the CRZ cross-section (6335100). B) Hydrothermal alteration assemblages and sulfide mineral distribution in the CRZ. The geologic key for this figure can be found in Fig. 4.3.  The breccia is internally zoned with a more polymictic, finer-grained core and monolithic jigsaw-fit facies on the eastern and upper margins (Micko et al., in review; chapters 2 and 3) that are interpreted to define a moderate westerly dip of the breccia body. Orthoclase-phyric syenites and a voluminous body of megacrystic orthoclase and plagioclase-phyric monzonite intrudes into the breccia parallel the breccia geometry. 134  A wedge-shaped, composite ore zone defines the CRZ. It developed in two mineralization events (Fig. 4.4B). In cross-section view, the Cu-enriched ore shell is about 300m in width and 400-450m in length. A weak, sulfide zonation pattern is recognized within the Cudominated and Au poor ore zone. Chalcopyrite with accessory bornite forms restricted, high grade centres dominantly located within the shallow eastern section of the ore zone. The highgrade centres are surrounded by a chalcopyrite dominated shell that extends down dip to the core of the CRZ. Outboard of this shell, chalcopyrite + pyrite dominate with a gradual transition into a peripheral sulfide-depleted zone. A pyrite outer shell, as mapped in the NGL, is not apparent. The shallow, western section of the mineralized shell is crosscut by late, post-mineral megacrystic orthoclase and plagioclase-phyric monzonites. Sulfide distribution and zonation are controlled by the host rock and timing of mineralization. The large chalcopyrite-dominated shell and smaller high grade chalcopyrite+ minor bornite centres are hosted in pseudoleucite-phyric trachyte and derivative clastic rocks and orthoclase (and pseudoleucite)-phyric syenites. These rock units are commonly altered with Kfeldspar, biotite, magnetite, hematite, and anhydrite, forming a potassic alteration assemblage. Chalcopyrite typically replaces biotite and magnetite, whereas bornite is associated with hematite. The Cu-enriched high grade shell also extends from the centre of the CRZ into the eastern margin of the hydrothermal breccia body. As in the NGL, Au-enrichment is associated with bornite that, in the CRZ, appears confined to clasts derived from potassic altered and mineralized rock units that compose the breccia wall rock. Clasts are cemented by hydrothermal andradite (Dunne et al., 1995) with a smaller compositional component of grossular, biotite and anhydrite as well as lesser magnetite, orthoclase, and diopsidic pyroxene. This calc-potassic alteration assemblage is roughly confined to the limits of the breccia body. Chalcopyrite + pyrite, the dominant sulfide phases introduced by the calc-potassic event, locally replaced biotite and magnetite of the cement assemblage, but more commonly form cement infill. The 135  distribution of abundant cement sulfides is constrained to the shallow eastern margin of the breccia body. Late SAC and propylitic alteration stages introduced additional pyrite that occurs as disseminated cubes or vein fill. These alteration assemblages overprint all older assemblages in the eastern margin of the CRZ.  4.4 Methodology Samples for a sulfur isotope analysis of the NGL and CRZ were derived from coarse crystalline chalcopyrite, pyrite, Au-bearing bornite and rare galena for δ34Ssulfide analysis, whereas samples for δ34Ssulfate analysis are derived from anhydrite only. Monomineralic powder samples sufficient for ICP-MS analysis were produced using a Dremel Multipro 225 T2 Flexshaft drill and analyzed at CODES, University of Tasmania, Australia. δ34Ssulfide+sulfate values were measured using both conventional (Robinson and Kasakabe, 1975) and laser ablation methods (Ohmoto and Goldhaber, 1997). Based on previous research by Wilson et al. (2007) at CODES an analytical uncertainty of ±0.1‰ is assumed. These were calculated from internal standards of homogenous galena from Broken Hill (δ34S = +3.40‰) and Rosebery (δ34S = +1.83‰) that were run with an SO2 reference gas of δ34S ≈Cañon Diablo Troilite (CDT). These internal standards were calibrated against international sphalerite standards IAEA NZ1 (δ34S = +1.83‰) and NBS 123 (δ34S = +4.34‰). Isotope measurements were performed on a VG Sira Series II mass spectrometer. Overall δ34Ssulfide samples (n=158) and sulfate samples (n=27) were collected and analysed (Table A3.1 and A3.2). In addition to the analytical undertainty defined above an additional quality controle has been applied based on the submission of duplicate and blank samples (n=30). The internal error defined is δ34S ≤ 0.42‰ (sigma 1) for both sulfide and sulfate samples. Geothermometric calculations on sulfide-sulfide and sulfide-sulfate pairs were 136  carried out using a “stable isotope fractionation calculator”, a freeware program, accessible at http://www.ggl.ulaval.ca/cgibin/isotope/generisotope.cgi. NovaGold Resources Inc. routinely analyzed 2.5 m lengths of split HQ (7cm diameter) and NQ (5.5cm diameter) diamond drill core at Galore Creek for their chemical composition using the “single acid digest” (aqua regia) analytical method (ALS Chemex: ME-ICP41) at ALS Chemex. Each interval was designed to terminate at lithological contacts, but did not take changes in hydrothermal alteration into account. Thus, produced pulp samples are representative of rock type, but may contain composite alteration assemblages that may cause some scatter in the data.  The analytical package chosen by NovaGold Resources Inc. results in a partial  digestion of minerals and therefore incomplete element analysis of 27 elements (Cohen et al., 2010); these data are thus unable to fully analyze the chemical dispersion around the porphyry centers. To investigate the elemental zoning more fully, duplicate pulp samples were collected on a 20 metre grid for the NGL and CRZ, and reanalyzed with a four acid ‘near total digestion’ method (ALS Chemex: ME-MS61m). Due to the grid sampling a representative set of moderately fresh to highly altered rock samples was collected. The combination of HF-HNO3HClO4-HCl dissolves nearly all minerals except the most resistive ones such as zircon (Cohen et al., 2010). A 48-element suite is analysed by inductively coupled plasma mass spectronometer (ICP-MS) and atomic emission spectronomter (ICP-AES) (Table 4.2). The combined analysis provides best possible detection limits for a wide range of elements commonly below their average crustal abundances (Table 4.2). Despite the limitation on dissolution of refractory minerals and the availability of higher research-quality digestion methods (e.g. use of Limetaborate digest), this analytical package more accurately replicates the analytical package utilized during exploration. Furthermore, elements shown to be anomalous around porphyry Cu  137  centers, such as Li (Chaffee, 1971; this study) are unavailable in complete digestion analytical packages.  Table 4.2: Suite of elements analyzed and reported minimum to maximum detection ranges for the ALS Chemex 4acid digestion analysis using analytical package ME-MS61m and instruments ICP-MS and ICP-AES. ME-MS61m analytical method - detection limits (ppm) Ag  0.01-100  Cu  0.2-10.000  Na  0.01-10%  Sr  0.2-10.000  Al  0.01-50%  Fe  0.01-50%  Nb  0.1-500  Ta  0.05-100  As  0.2-10.000  Ga  0.05-10.000  Ni  0.2-10.000  Te  0.05-500  Ba  10-10.000  Ge  0.05-500  P  10-10.000  Th  0.2-10.000  Be  0.05-1.000  Hf  0.1-500  Pb  0.5-10.000  Ti  0.005-10%  Bi  0.01-10.000  In  0.005-500  Rb  0.1-10.000  Tl  0.02-10.000  Ca  0.01-50%  K  0.01-10%  Re  0.002-50  U  0.1-10.000  Cd  0.02-1.000  La  0.5-10.000  S  0.01-10%  V  1-10.000  Ce  0.01-500  Li  0.2-10.000  Sb  0.05-10.000  W  0.1-10.000  Co  0.1-10.000  Mg  0.01-50%  Sc  0.1-10.000  Y  0.1-500  Cr  1-10.000  Mn  5-100.000  Se  1-1.000  Zn  2-10.000  Cs  0.05-500  Mo  0.05-10.000  Sn  0.2-500  Zr  0.5-500  A second data set was also available based upon the metallurgical testing of mineralized rocks from a varying locations and rock types. In most cases at Galore Creek, none of the original drill core chosen for MET sampling is retained and information about the host lithologic type is sparse. Nevertheless, MET samples are commonly associated with high overall metal content and are thus strongly representative of the effects of hydrothermal alteration and mineralization in the system. Therefore, representative MET pulp samples were collected,  138  analyzed, and added to the whole rock geochemical dataset in order to quantify the spatial effects on hydrothermal alteration.  4.5 Sulfur isotope distribution Sulfur isotopic research on alkalic porphyry deposits in Canada, Australia, and the Philippines suggests that a systematic, vertical, and lateral zonation surrounds some mineralized porphyry ore bodies (Wilson et al., 2007). In general, the sulfur isotopic compositions of sulfide minerals in porphyry deposits are typically reported to be near zero, indicating magmatic derivation (e.g. Fields et al., 1966; Ohmoto, 1972). However, individual calc-alkalic and alkalic systems such Tintic (Utah, USA) and Cadia (NSW, Australia) respectively appear to have largely negative values with ranges between –2 and -10‰ δ34Ssulfide (Fig. 4.5). Even lower values have been reported for Galore Creek (B.C., Canada), and Ridgeway (NSW, Australia) (Harper (2000); Wilson (2003); Wilson et al. (2003); Wilson et al. 2007a; this study).  139  Figure 4.5: Schematic presentation of sulfur isotope data of alkalic and calc-alkalic porphyry deposits worldwide. Modified after Barnes (1979) and Ohmoto and Rye (1979). Additional data concerning alkali porphyry deposits with the exception of Galore Creek are derived from Wolfe (1994), Heithersay and Walshe (1995), Harper (2000), Wolfe (2001), Lickfold (2002), Harris and Golding (2002), Lickfold et al. (2003), Wilson (2003), Wilson et al. (2003), Deyell and Tosdal (2005), Reese et al. (2005), Wilson et al. (2007a), Pass, (2010), Bath and Cooke (2008).  In these deposits, the most negative values typically are present towards the top of the mineralized intrusions and breccia bodies, with a return to near-zero values with distance upwards and/or outwards from the mineralized zone. The resulting gradient led to the proposal that sulfur isotopes may provide a vector toward the sulfide core of the system (Wilson et al., 2007). In addition to building gradients, the isotopic composition of sulfur-bearing minerals 140  provides information on the overall intrinsic physiochemical conditions and mechanisms of ore deposition, such as temperature and oxidation potential, and the sources of sulfur in ore forming fluids (Ohmoto and Rye, 1979). However, in order to fully understand the implications of the δ34S data, a systematic paragenetic study of the magmatic and hydrothermal history is essential (Deyell and Tosdal, 2005). This is of particular relevance in the CZ deposit, where two phases of mineralization overlap to form the composite ore shells (Micko et al., in review; chapter 3). 4.5.1  North Gold Lens  All δ34Ssulfide and δ34Ssulfate values (Fig. 4.7A and 4.7B) are derived from in equilibrium chalcopyrite, bornite, pyrite, and anhydrite samples deposited during early main stage potassic alteration and during late main stage calc-potassic alteration (Fig. 4.6; Table A.3.1). The δ34Ssulfide values of the early stage range from -17.13‰ to -4.22‰ and δ34Ssulfate values lie between +4.03‰ and +6.21‰ (Fig. 4.7A). Late stage δ34Ssulfide values range from -10.33‰ to 5.40‰ and δ34Ssulfate values lie between +3.26‰ and +6.91‰ (Fig. 4.7B).  141  Figure 4.6: Examplatory sulfide and sulfate samples of the NGL and CRZ in thin section (to the left) and hand sample (to the right). A) GC04-0501 (487.50m) is representative of the potassic stage 2a sulfide+sulfate mineral assemblage that consists of texturally in equilibrium chalcopyrite, bornite and anhydrite with minor magnetite. B) GC06-0732 (296.70m) shows a large amalgamation of texturally in equilibrium pyrite and chalcopyrite with anhydrite common for the calc-potassic stage 2b.  142  Figure 4.7: A) Contoured values of δ34S (‰) of sulfides and sulfates derived from the early main stage potassic alteration assemblage in the NGL. B) Contoured values of δ34S (‰) of sulfides and sulfates derived from the later main stage calc-potassic alteration assemblage in the NGL. C) Au+Cu grades and sulfide distribution, overlapped by overall potassic and calc-potassic mineralization derived δ34S (‰) contours.  Highly negative δ34Ssulfide values (-17.13‰ to -11.65‰) of the early mineralization event are localized in small centers throughout the NGL and correlate with the high-grade Au-enriched ore shell (Fig. 4.7C). The highest Au grades (>2.0 to 1.0g/t Au) correlate with δ34Ssulfide values ranging from -17.13‰ to -7.86‰ (average of -10.66‰), including all of the δ34Ssulfate values (average of +4.88‰). The negative S-isotopic footprint and the high grade Au-enriched ore shell 143  coincide with intensively potassic altered, felsic rock units such as pseudoleucite-phyric trachyte and derivative clastic rocks as well as orthoclase (and pseudoleucite)-phyric syenite intrusions in the deep western and central portion of the NGL. The contoured S-isotopic values are also oriented sub-parallel to the host rocks and intrusions (dip: 45-60°W), but do not cross the lithologic contact between pseudoleucite-phyric trachyte and augite-phyric basalt host rock (Fig. 4.7A). Surrounding the highly negative δ34Ssulfide values and Au-enriched ore shell are moderately negative δ34Ssulfide values ranging between -6.61‰ to -4.22‰ (average of -5.87‰). These form a S-isotopic footprint that correlates with the Cu-dominated halo (>1.5 to 0.5 wt% Cu; Figs. 4.7A and 4.7C) and overlaps with orthoclase-phyric trachyte, augite-phyric basalts, and orthoclase (and pseudoleucite) -phyric syenites that directly underlie the felsic to mafic host rock contact. The overall footprint of these values is broader, but includes the very negative δ34Ssulfide values of the high-grade zone. Together they show a moderate dip to the west (Fig. 4.7A). The localized high grade Au center in the shallow central to eastern section in the NGL (Fig. 4.7C) cannot be directly be attributed to either the early or late mineralization event, due to the lack of available diamond drill core, as it was previously removed for metallurgical (MET) sampling. However, based on NovaGold Resource drill core logs, the dominant alteration assemblage is potassic. The most negative δ34Ssulfide value associated with the late mineralization event is 10.33‰, and corresponds to the Au-enriched ore shell in the central portion of the NGL. The dominant δ34Ssulfide values range between -9.48‰ and -7.13‰ (average of -8.77‰) and in equilibrium δ34Ssulfate values show an average of 5.27‰ (Figs. 4.6 and 4.8). These values correlate with Cu-dominated halo and lower overall ore grades (>0.5wt% Cu). In addition, the Sisotopic footprint overlaps the hydrothermal breccia and mafic volcanic rocks in the deep 144  western and central portion of the NGL. With greater distance from the hydrothermal breccia body and the center of calc-potassic alteration in the east of the NGL, the δ34Ssulfide values become slightly less negative with an average of -6.19‰ and the associated Cu-grade drops dramatically. The overall negative S-isotopic footprint of late stage mineralization arguably shows a westerly inclination oriented on the felsic to mafic host rock boundary similar to the δ34S values of the early mineralization stage.  Figure 4.8: Distribution of Cu (wt%) and Au (g/t) concentration relative to δ34S (‰) values both in sulfide and sulfate samples. Note that the dominant number of samples associated with high metal values fall into a δ34S range of -10 to -5‰ for sulfides and +4 to +7‰ for sulfates (highlighted in grey).  The outer SAC/propylitic zone is characterized by sparsely disseminated pyrite and pyrite-filled veins that crosscut all previous assemblages. Associated δ34Ssulfide values for the pyrite range between +1.08‰ and +0.04‰, and are much closer to common magmatic S-isotope values of ~0‰ (Ohmoto and Rye, 1979; Wilson et al., 2007). Pyrite carries no Au grade. 4.5.2  Central Replacement Zone  All δ34Ssulfide and δ34Ssulfate data (Fig. 4.9A and 4.9B) are derived from chalcopyrite, bornite, pyrite, galena, and anhydrite samples deposited during early main stage potassic 145  alteration and during later main stage calc-potassic alteration and associated mineralization events (Table A.3.2). Potassic δ34Ssulfide values range from -15.10‰ to -4.03‰, whereas calcpotassic δ34Ssulfide values lie between -14.34‰ and -5.76‰ and δ34Ssulfate values between +4.55‰ and +8.07‰ (Fig. 4.9B).  146  147  Figure 4.9: A) Contoured values of δ34S (‰) of sulfides and sulfates derived from the early main stage potassic alteration assemblage in the CRZ. B) Contoured values of δ34S (‰) of sulfides and sulfates derived from the later main stage calc-potassic alteration assemblage in the CRZ. C) Au+Cu grades and sulfide distribution, overlapped by overall potassic and calc-potassic mineralization derived δ34S (‰) contours.  The δ34Ssulfide values associated with the early mineralization event do not form distinct haloes nor a systematic arrangement with the ore zone (Fig. 4.9A). The somewhat chaotic distribution stands in contrast to the NGL (Fig. 4.9A). In the CRZ, both highly to moderately negative δ34Ssulfide values define localized centers that do not correlate with Au-enrichment, but do with elevated Cu >0.5 wt% Cu (Fig. 4.9C). In the shallow eastern portion of the CRZ, chalcopyrite and bornite were derived from the early mineralization stage, and is directly associated with elevated Au grade. Unfortunately, due to the finely disseminated nature of the sulfides, S-isotopic analytical data could not be obtained. Highly negative δ34Ssulfide values derived from the late mineralization event are located in the deep, western portion of the hydrothermal breccia body, and range from -14.34‰ to 11.13‰ (average of -12.22‰); however, they are only poorly correlated with Cu or Au grade (Fig. 4.9B). Moderate δ34Ssulfide values are between -9.32‰ and -7.12‰ (average of -7.84‰) and δ34Ssulfate values between +8.07‰ and +4.55‰ (average of 5.85‰). These correlate with Cuenrichment (>1.0 to 1.5 wt% Cu) in the shallow central eastern portion of the hydrothermal breccia body and compare with Cu-related, late mineralization stage S-isotopic signatures obtained in the NGL (Fig. 4.8). The least negative isotopic signatures range between -6.53‰ to 5.47‰ (average of -6.18‰), and are from the vicinity of and beyond the eastern margin of the hydrothermal breccia. The overall sulfide derived S-isotopic values in the CRZ progressively change from highly negative in the deep core of the hydrothermal breccia body (-14.34‰) to moderately negative at the lithologic contact in the east (-5.47‰), thus forming a gradient. This gradient is oriented sub-parallel to the orthoclase (and pseudoleucite-phyric) syenite intrusions in the CRZ, and follows the same 45 to 60°W dip of the S-isotopic footprint and ore shell in the NGL. Scattered SAC and propylitic alteration assemblages in the CRZ are commonly associated with coarse, barren pyrite veins that crosscut all previous alteration assemblages. 148  Their average δ34Ssulfide value is -3.62‰ and thus, more negative than the ones observed in the NGL. 4.5.3  Geothermometric analysis  If the isotopic differences between sulfates and sulfides represent effects of primary equilibrium isotopic exchange reactions at the time of mineral deposition, then isotopic temperature estimates may be determined from the degree of S34-isotope fractionation (ΔA-B = δ34SA-δ34SB = ~1000lnαA-B ) between the co-genetic mineral pairs (Ohmoto and Rye. 1979; Fields et al., 2005). The sulfur isotope geothermometer of Kajiwra and Krouse (1971) applied to three sulfide-sulfide pairs that consist of pyrite-chalcopyrite samples (Table 4.3) results in a temperatures range from 199°C at the lowest in one potassic sample to 287°C and 522°C in the calc-potassic samples. In contrast, the temperatures ranges for sulfate-sulfide pairs derived from the potassic samples range from 456°C to 591°C, which overlaps that of sulfate-sulfide pairs from calc-potassic samples that range from 454°C to 573°C (Table 4.3). Temperature ranges were calculated on the basis of fractionation equations from Ohmoto and Rye (1997), for sulfateH2S, and Li and Liu (2006), for sulfide-H2S. The low temperatures derived from the pyritechalcopyrite fractionations suggest that chalcopyrite may have undergone retrograde reactions (Fields et al., 2005). The anhydrite-pyrite pairs provide the highest temperatures, whereas the anhydrite-chalcopyrite and bornite pairs the lowest. Nonetheless, the isotopic temperature estimates agree with fluid inclusion temperatures that range from 407°C to 561°C from garnets (Dunne et al., 1995). They also correlate with common temperatures for porphyry mineralization (Lang et al., 1995; Ulrich et al., 1999; Wolfe, 2001; Lickfold et al., 2003; Wilson et al., 2003; Landtwing et al., 2010).  149  Table 4.3: Sulfur isotopic temperature estimates for sulfide-sulfide and sulafte (anhydrite)-sulfide pairs from the NGL and CRZ. δ34SCDT (‰)  Alteration stage  Location/ DDH/depth  Sulfide  ΔA-B =  Temp.  Mineral pair  δ SA - δ SB  °C  34  34  Sulfate (anh)  North Gold Lens GC0549-352.50  potassic  cp  -9.59  4.03  cp/anh  -13.62  553  GC0558-387.50  calc-potassic  cp  -8.93  6.91  cp/anh  -15.84  454  GC0573-330.30  potassic  py  -6.29  6.21  py/anh  -12.50  591  potassic  cp  -8.30  py/cp  2.01  199  calc-potassic  bn  -9.69  bn/anh  -16.02  456  calc-potassic  cp  -7.64  py/cp  -0.71  522  py  -6.93  GC0734-415.20  6.33  Central Replacement Zone GC0488-416.60  GC0568-179.50  calc-potassic  py  -7.56  5.35  py/anh  -12.91  565  GC0568-417.00  calc-potassic  cp  -7.93  5.33  cp/anh  -13.26  573  GC0732-23.00  calc-potassic  cp  -9.32  4.55  cp/anh  -13.87  540  GC0732-198.00  calc-potassic  py  -6.56  py/cp  1.48  287  The presence of sulfate with sulfides provides the means of approximating δ34SƩS for the hydrothermal system. Due to the close temperature and 34S range between potassic and calcpotassic samples (Table 4.3), we can assume the same, or at least a similar, composition hydrothermal fluid and sulfur source. Fractionation theory suggests that the δ34SƩS must fall between that of the  34  S-enriched anhydrite (mean = 5.53‰) and that of relatively  34  S-depleted  sulfides (mean = -8.07‰). The mid-value here is δ34SƩS = -2.54‰, and falls into the common estimated range for magmatic sulfur of -3 to 1‰ (Ohmoto and Rye, 1979). A more precise estimate for δ34SƩS calculates the relative abundance of oxidized to reduced sulfur in the hydrothermal system (Ohmoto, 1972, 1986; Ohmoto and Rye, 1979; Ohmoto and Goldhaber, 1997; Fields et al., 2005). These abundances are represented by mole fractions of oxidized (XSO42-) and reduced (XH2S) sulfur components that sum to unity with respect to total sulfur 150  (Fields et al., 2005). The proportions of these two components is given by R (=XSO42- / XH2S) and thereafter by the sulfate mole fraction (XSO42- = R/ (R+1)). Field and Gustafson (1976), Field et al. (1983), and Kusakabe et al. (1984) reported that regression analysis of the δ34S vs. Δ34SSulfate-Sulfide data for a suite of sulfate-sulfide mineral pairs should form two linear and converging trend lines. Due to the temperature dependency of isotope fractionation, the point of convergence of these two lines extrapolated to high temperature should define the value of δ34SƩS, and the slopes of the upper and lower lines should approximate the XSO42- and the XH2S of the system respectively (Field et al., 2005). The positive slope relates to the sulfate mole fraction (XSO42- = 1-m), whereas the negative one relates to the sulfide mole fraction (XH2S = 1+m). In a common linear function (y=mx +b), m defines the slope and b the intercept, represented by the two converging lines. Intercept b on the y-axis also define δ34SƩS. The most reliable data points in regards to isotopic equilibrium are derived from anhydrite-pyrite mineral pairs of the calc-potassic alteration assemblage (Fig. 4.6). These form the foundation of subsequent calculations (Fig. 4.10). The positive slope defines the oxidized sulfur component as XSO42- = 0.80, whereas the negative one defines the reduced sulfur component as XH2S = 0.20. The point of convergence and thus δ34SƩS lies at ~-3‰, which correlates well with the mean estimate of -2.54‰ identified above. Assuming an approach of isotopic equilibrium between sulfate and sulfide components, the angle between converging lines of regression should always be 45° (Fig. 4.10). Concerning our dataset, this is not the case, and implies that R was variable or that δ34SƩS of the system changed due to contamination from an isotopically distinct extraneous source (Field and Gustafson 1976; Field et al., 1983; Ohmoto et al., 1983; Seal et al., 2000; Field et al., 2005; Wilson et al., 2007).  151  Figure 4.10: Plot of δ34S (‰) values for associated sulfate (anhydrite) and sulfide minerals pairs versus the Δ value of the pairs. The convergence of the slopes of the two regression lines offers an approximation of the bulk sulfur isotopic composition (δ34SƩS) and the proportions of oxidized to reduced sulfur (XSO42- to XH2S) in the hydrothermal system (after Fields et al., 2005).  4.6 Lithogeochemistry The geochemical analysis of the host rocks in the NGL and CRZ can provide a template for the differentiation of individual rock units based on the variations in primary igneous chemistry. It can also define which elements are anomalous and the magnitude of anomalism caused by hydrothermal alteration. The combined results may define spatial scale of zonations that relate back to chemical variables such as pH, fO2, and aH2S that ultimately control Cu and other metal grade distributions within the hydrothermal system. 4.6.1  Variations in primary igneous chemistry  Igneous compositional differences and hydrothermal alteration are the major material transfer processes that affected the Galore Creek rocks. In intensely altered rocks such as those at Galore Creek, elements representative of primary host rock composition that are immobile or 152  high field strength elements (HFSE), such as Ce, Cr, Hf, La, Nb, Sc, Ta, Th, Ti, Y, and Zr, can be utilized to discriminate primary compositions (Ciftci et al., 2005; Gale et al., 2002). These elements are commonly associated with silicate and phosphate host minerals, formed during alteration, that are not refractory during acid dissolution. Zirconium, however, is the exception, as Phanerozoic zircon is generally refractory and may not completely dissolve in the 4-acid geochemical package. Therefore, Zr may be under-reporting to the assay values, and thus must be used with care. Reported Zr concentrations in this study’s dataset range from 3 to 125ppm (Fig. 4.11). Abundances > 40 ppm are consistent with results of an earlier MDRU study that range 40 to 225ppm for the syenitic to monzonitic intrusive suites (Stanley et al. in 1992). That data was acquired via X-Ray Fluorescence (XRF) methods. The low Zr abundances are consistent with the general lack of zircons in the rocks.  153  Figure 4.11: Harker variation diagrams identifying the SiO2 (wt%) versus Ti, Y, Th, Nb, and Zr (ppm) concentrations and potential igneous fractionation paths. See inserted key for colour and symbol code.  154  Harker diagrams provide a means to evaluate whether the low Zr values encountered in either study reflect the primary composition of host-rocks (Fig. 4.11). The analytical package utilized does not report SiO2, but accounts for the remainder of the major elements. Aluminum, Ca, Fe, K, Mg, Na, P, S, and Ti values were recalculated as weight percent values of the oxides, and summed. An allowance was made for loss on ignition (LOI). Due to the silica undersaturated nature of the host rocks and the presence of hydrous and carbonate-bearing minerals such as gypsum (hydrated anhydrite) and calcite, the LOI value is estimated high and calculated at approximately 3.5% for mafic rock units and 1.7% for felsic to intermediate rock units. SiO2 was derived via the formula: 100 – (sum of major elements)*1.05. This estimate should be within 2 to 4% of the actual SiO2 value. The Harker diagrams (Fig. 4.11) present all rock types in the NGL and CRZ (Table 4.1) except for the fine-grained sandstone to siltstone and ribbon chert, of which no analytical data is available. Furthermore, analytical data from the garnet-pyroxene-cemented breccia was not considered at this stage, due to the hydrothermal origin (Micko thesis, chapter 2 and 3). On a broad scale, the elements Ti, Th, Y, and Nb reflect host rock composition that trend from the oldest mafic to the younger felsic volcanic rocks as well as the syenitic and monzonitic intrusive suites.  The SiO2 vs. Ti, and Y plots show a cluster of values that forms a weak  negative trend from mafic to felsic and intermediate rock units, whereas SiO2 vs. Th, and Nb plots show a strong positive trend from mafic to felsic volcanic rocks and for the intrusive suites. All trends may reflect fractionation in primary host rocks. Of note are two separate groups of monzonitic intrusions that are also distinguished in the field. Some data-scatter along the trendlines is assumed to be due to hydrothermal alteration effects. The SiO2 vs. Zr plot shows a similar, positively trending assay value distribution, and depicts the separate monzonitic intrusive suites. However, the assay values derived from pseudoleucite-phyric trachyte and derivative rocks appear to be underreporting Zr concentrations. Either mass gain in the felsic 155  volcanic rocks due to hydrothermal alteration may be in part responsible for the low Zr, or Zr is underreporting due to the refractory nature of zircon. Thus, further use of Zr as petrogenetic discriminator is limited to mafic rock units and monzonitic intrusive suites. Scandium is generally immobile during metasomatism; therefore, Sc-scatterplots effectively discriminate not only the effects of alteration, but can also distinguish between samples of felsic, intermediate, mafic, and even ultra-mafic composition (Halley et al., 2006; Prendergast, 2007). Overall, two distinct groups of compositionally variable host rocks are identified by Sc-content only. These are further divided into several sub-groups on the basis of Sc vs. other immobile element plots. Mafic rocks Sc values in mafic rock units, including the orthoclase-phyric trachyte are higher than the values in felsic to intermediate rock units. An empirically defined boundary lies at Sc = 20ppm. The hornblende and plagioclase-phyric basaltic andesite and augite-phyric basalt range from 20 to 50ppm, whereas Sc values for orthoclase-phyric trachyte lie between 20 and 35ppm (Fig. 4.12). Despite the overlap of values, there appears to be a slight compositional variation between the rock units.  156  Figure 4.12: Sc (ppm) versus Ti (wt%), Y, Th, Nb, and Zr (ppm) scatterplots mafic and felsic to intermediate composition in host rocks and hydrothermal affinities. See inserted key for colour and symbol code.  157  The elevated Sc content of the orthoclase-phyric trachyte and close geochemical association with the hornblende and plagioclase-phyric basaltic andesite suggests that this rock unit may have been miss-identified in the NGL due to intense alteration. The unit may represent either a strongly altered version of hornblende and plagioclase-phyric basaltic andesite or a separate, unidentified rock unit. Sc-scatterplots with Th, Nb, and Zr are relatively depleted, and show a very tight range for all three mafic rock units (Fig. 4.12). The best discriminators between the individual mafic units are Ti and Y. They form a positive trend with Sc in the Augite-phyric basalt. The orthoclase-phyric trachyte and hornblende and plagioclase-phyric basaltic andesite display a tight range of Ti values and thus a steeper yet distinct trend with Sc. Felsic to intermediate rocks Sc values in felsic to intermediate rock units are low overall; nevertheless, Sc values ranging between <1 and 10ppm discriminate felsic pseudoleucite-phyric trachyte and derivative clastic rocks and the syenite intrusive suite from the intermediate monzonitic suite that dominantly ranges from 5 to 18ppm (Fig. 4.12). The Sc vs. Ti and Y scatterplots show a moderately tight range for all felsic to intermediate rock units, yet distinguishe a monzonitic rock suite as compositionally different due to a positive trend with Sc. This parallels the trend of the augite-phyric basalt, and is not repeated in pseudoleucite-phyric trachyte and derivative clastic rocks and the syenite intrusive suite. The Sc-scatterplot with Nb and Th are the best discriminator between the felsic to intermediate rock units. They define four main rock types, including two sub-units in the monzonitic suite previously defined in the Harker diagrams (Fig. 4.11). Sc vs. Zr values for pseudoleucite-phyric trachyte and derivative clastic rocks form a tight cluster due to the underreporting of assay values in this particular rock unit. Nevertheless, both monzonitic subunits are clearly defined. 158  In few cases, extremely elevated assay values of Y, Nb, and Th with low overall Sc are present in the felsic rock units. These are believed to reflect apatite and were removed from the analysis. Igneous and hydrothermal apatite is an accessory mineral in the host rocks’ groundmass and forms small, cross-cutting veins with limited spatial distribution (Liaghat and Tosdal, 2008). In particular, the hydrothermal apatite is a sink for HFSE and REE. When analyzed, these veins lead to local assay value peaks that are not representative of the overall rock composition. 4.6.2  Variations in immobile elements due to alteration  Hydrothermal alteration assemblages in porphyry environments reflect the interaction of host rocks with highly oxidizing fluids (Jensen and Barton, 2000; Seedorff et al., 2005; Micko et al., in review; chapters 3 and 5). Thus, the spatial distribution of alteration assemblages provides not only valuable indication of the degree of hydrothermal alteration, but also relative reductionoxidation (redox) gradients within the hydrothermal system. The Sc vs. Fe, Ti, and V scatterplots (Fig. 4.13) constrain the degree of hydrothermal alteration that affected individual rock units and the relative oxidation state of the rock samples (Halley et al., 2006; Neumayr et al., 2006; Walshe et al., 2006).  159  Figure 4.13: Sc (ppm) versus (A) Ti (wt%), (B) Fe and (C) V (ppm) - scatterplots differentiate between primary magmatic, hydrothermal affinities and degree of oxidation of host rocks. Note that hydrothermal breccia and MET samples have been added to the dataset.  Sc substitutes for Fe2+ in minerals such as amphiboles, pyroxenes, and biotite, but does not partition into Fe3+-bearing silicates or oxides. Therefore, samples that show Sc-deficiencies in combination with Fe-enrichment contain Fe3+ and were derived from rocks that have undergone hydrothermal alteration. The Sc vs. Ti and V plots are also affected by oxidation 160  based on the assumption that primary Ti is relatively immobile during hydrothermal alteration and should retain a consistent trend with primary Sc (Halley et al., 2006; Neumayr et al., 2006; Walshe et al., 2006). Vanadium also substitutes into Fe-bearing minerals and should therefore show a linear correlation with Sc rocks except under oxidizing conditions (Fig. 4.13C). In such cases, V is mobilized in a high valence state (V3+, 4+, 5+) that substitutes into other Fe and/or Ti bearing minerals such as andradite, magnetite, coulsonite (FeV2O4), and rutile (Scott et al., 2005). Therefore, deviations from a linear relationship between Sc and V reflect an oxidized environment. In order to quantify the effects of metasomatism on host rocks in the NGL and CRZ, the overall results of the Sc vs. Fe, Ti, and V alteration scatterplots were compared to the observed primary and alteration mineralogy. For this, the analytical values derived from the hydrothermal breccia and metallurgical samples (MET) have been added to the dataset. Mafic rock units The hornblende and plagioclase-phyric basaltic andesite and the orthoclase-phyric trachyte are enriched in Sc and Fe, but depleted in Ti and V. On all plots (Fig. 4.13), the elements show a relatively tight compositional range, yet show a steep positive trend with Sc indicative of a primary mineralogy dominated by hornblende and orthoclase. The only slight scatter in Fe suggests the hydrothermal alteration did not add significant Fe, and presence of Fe2+ and Fe3+-bearing alteration minerals such as biotite, magnetite, and andradite, as well as Fesulfides (see chapter 3; Fig. 4.13B). The steep trend between Sc and V implies little V mobility under reducing to moderately-reducing fO2 conditions (Fig. 4.13C). The rock units appear to have undergone a small amount of hydrothermal modification to their primary compositions. The augite-phyric basalt is enriched in Sc, Ti and Fe, but relatively depleted in V. Titanium forms a positive trend with Sc and shows little to moderate scatter (Figs. 4.10 and 4.12). In contrast, the Sc vs. Fe plot presents a less defined trend with much wider scatter (Fig. 161  4.13B). Ti and Fe values that share the common trend with Sc are indicative of primary Fe2+ and Ti-bearing minerals such as pyroxene, biotite, ilmenite, and/or Fe-sulfides. The remainder of the scattered values suggest the presence of hydrothermally derived Fe2+, Fe3+, but few Ti-bearing minerals such as biotite, andradite, magnetite, titanite, rutile, and Fe-sulfides (Figs. 4.13A and 4.13B). Despite the overall depletion in V, the Sc vs. V scatterplot shows a steep trend that implies little V mobility (low valence state) under moderately oxidizing fO2 conditions (Fig. 4.13C). The rock unit has undergone a moderate amount of hydrothermal modification of the original composition. Felsic rock units A large portion of the pseudoleucite-phyric trachyte and derivative rocks (Fig. 4.12) and the syenitic intrusive suite are relatively depleted in Sc, Ti, Fe, and V, which is indicative of the primary mineralogy being dominated by orthoclase and various feldspathoids. Slightly elevated Ti, Fe, and V values do not form a common trend with Sc, and are associated with a hydrothermal mineral assemblage of Fe3+ and/or Ti-bearing minerals such as biotite, andradite, magnetite, hematite, titanite, and rutile. Vanadium values may suggest an increased valence state and mobility under more strongly oxidizing fO2 conditions (Fig. 4.13C). A moderately high oxidation state implies a higher degree of hydrothermal alteration that may not be expressed by the Fe3+ content, but associated with K-enrichment. The monzonitic intrusive suite is depleted in Sc, Fe, and V, but shows enrichment in Ti. Titanium, Fe, and V form a distinct trend with Sc (Fig. 4.13), which suggests the presence of primary Fe2+ and Ti-bearing minerals such as biotite, hornblende, magnetite, ilmenite, and Fesulfides. Only a few values on the Sc vs. Fe and V plot depart from this trend (Figs. 4.13B and 4.13C). These are suggestive of the effects of hydrothermal alteration and crystallization of Fe3+bearing minerals such as biotite, magnetite, garnet, and epidote. The steep trend between Sc and V implies limited V mobility under moderately oxidizing fO2 conditions (Fig. 4.13C). The rock 162  units appear to have undergone neglible compositional modification during hydrothermal alteration. MET samples, hydrothermal breccias and felsic rocks The hydrothermal breccia, MET samples, and a smaller portion of the pseudoleucitephyric trachyte and derivative clastic rocks (Fig. 4.13) are depleted in Sc, moderately enriched in Ti, and strongly enriched in Fe and V. None of the elements form a trend with Sc. This implies that the high concentrations are associated with Fe3+, Ti, and V-bearing, hydrothermal minerals such as biotite, andradite, hematite, magnetite, titanite, rutile, and potentially coulsonite. Extremely high V values also suggest increased V mobility (increased valence state) under strongly oxidizing conditions and indentify these rock units as the most strongly altered ones in the system (Fig. 4.13C). 4.6.3  Variations in alkali elements due to alteration  Major element molar ternary and molar ratio plots can examine not only igneous compositional changes, but also the superposed effects of hydrothermal alteration. Major elements prominent in the NGL and CRZ are K, Al, and Ca associated with igneous and/or hydrothermal mineral assemblage of K-feldspar, biotite, sericite, diopside, andradite, and anhydrite. Potassium, Al, and Ca were recalculated as general element ratios. Assays on a weight percent basis are divided by the atomic weight of each element, normalized to 100%, and plotted on a K-Al-Ca molar ternary plot (Figs. 4.14A and 4.14B).  163  Figure 4.14: A) Molar ternary K-Al-Ca and (B) molar K-Al-Ca ratio plot identifying the projected mineralogy of lithologic units as well as potential fractionation trends. C) Molar ternary K-Al-Ca and (D) molar K-Al-Ca ratio plot identifying the dominant hydrothermal mineral assemblages with the help of element ratio tie lines. See inserted key for colour and symbol code.  164  The K-Al-Ca molar ternary plot defines distinct compositional fields for all rock units in the NGL and CRZ (Fig. 4.14A). The mafic rock units are located in the K-Al-Ca-dominated center, and trend towards the felsic volcanic host rock units and syenitic to monzonitic intrusive suites in the K-Al-enriched and Ca-depleted portion of the ternary plot. This trend reflects in part the primary igneous compositional changes from older mafic to younger felsic and intermediate rock units (see also Fig. 4.11). Changes in alkali contents due to alteration are superposed on the igneous compositional variations and lead in some cases to a departure of values from the original trend-line. The observed trend is towards K and K-Al enrichment in the felsic rock unit, in particular the monzonitic intrusive suite and MET samples. The breccia samples form a continuation of this field towards the Ca-dominated portion of the plot. In order to classify mineralogical assemblages responsible for the observed trends, molar Ca/Al vs. K/Al ratio plots were employed. The general element ratios were considered on the basis of the relative number of atoms of each element, and compared to the ratios within mineral formulae. Orthoclase has K and Al in a ratio of 1 to 1. Similarly, muscovite has K and Al in a ratio of 1:3, whereas grossular has a ratio of 3:2. Molar ratios of K/Al (K feldspar, biotite, and muscovite), Ca/Al (grossular) were calculated and allowed the reconstruction of four associated mineral assemblages (Figs. 4.14C and 4.14D). A portion of the pseudoleucite-phyric trachyte-derived samples, the dominant part of the syenitic intrusions and MET samples are clustered below the biotite-K-feldspar-grossular tie-line (Figs. 4.14C and 4.14D) and trend towards biotite-K-feldspar, and muscovite composition (potassic 1). The remainder of the rocks and the monzonitic intrusive suite are more closely linked with the sericite-grossular tie-line (sericitic; Figs. 4.14C and 4.14D). The mafic rock units, including the orthoclase-phyric trachytes, form a cluster in the center of the plot on and around the biotite-K-feldspar-grossular tie-line. Several values plot below the tie-line, which implies the presence of additional K-bearing minerals such as muscovite. In contrast, values 165  above the tie-line (Figs. 4.14C and 4.14D) indicate additional Ca-bearing minerals such as andraditic garnet, diospide, epidote, and anhydrite (potassic 2). As with the mafic rock units, the hydrothermal breccia samples are distributed along and above the biotite-K-feldspar-grossular tie-line, but trend more strongly towards a grossular component. The dominant portion of the values plot above the tie-line (Figs. 4.14C and 4.14D), which implies an addition of Ca-rich minerals as described for the mafic rock units (calc-potassic). The molar-based classification of mineral types from the chemistry form the basis of mineral assemblage distribution maps that reflect lithologic and alteration zonation as well as hydrothermal fluid dispersion patterns. The four major hydrothermal alteration mineral types (potassic 1, potassic 2, calc-potassic, and sericitic) vary laterally in the NGL and CRZ (Fig. 4.3 and 4.4). The lateral distribution of the inferred mineral assemblages is evident on a combined cross-section oriented on the Easting and Northing values of the diamond drill holes (Fig. 4.15). The calc-potassic mineral assemblage trends from the deep western base of the combined crosssection to the center and forms small outliers in the shallow eastern section. This overlaps with the shallow level mafic rock units of the NGL distributed along the mafic to felsic lithologic contact as well as the hydrothermal breccias body (Fig. 4.15). The mineral assemblage potassic (1) forms a broad footprint that engulfs much of the center of the combined section, and correlates with a portion of the pseudoleucite-phyric trachyte and derivative rocks, syenitic intrusions, and the apex of the hydrothermal breccias body in the CRZ that in combination hosts the dominant Cu-Au grade in the system (Fig. 4.15). Assemblage potassic (2) forms a lens that is thin in the center, widens towards the east, and is exclusively linked with the mafic rock units in the NGL (Fig. 4.15). The sericitic assemblage is separated in two groups. One is centered on the monzonitic intrusive suites and trends from the shallow western to the shallow central portion of the section, where it tapers out. The second group is hosted in pseudoleucite-phyric trachyte and derivative rocks and engulfs much of the east (Fig. 4.15). 166  Figure 4.15: Attribute map identifying the distribution of the four main minerals assemblages defined by the molar K-Al-Ca ternary and ratio plot on the combined cross-section of the NGL and CRZ. The outline of the NGL crosssection is depicted in grey and spatially set behind the CRZ highlighted in black. See inserted key for the colour and symbol code.  The combined mineral footprints show a distinct zonation pattern with the calc-potassic and potassic (1) alteration assemblages in the core, flanked by potassic (2) and sericitic assemblages. In addition, it is oriented sub-parallel to the inclined geologic framework (dip 45° to 60ºW), which implies a strong lithologic control on hydrothermal fluid flow as well as on subsequent mineral assemblages and their chemical composition (Figs. 4.3, 4.4, and 4.15). 4.6.4  Pathfinder element distribution  Anomalous pathfinder element values are controlled by host rock mineralogy; therefore, if they are correlated with the dominant silicate mineral assemblages identified in the molar  167  abundance plots above, they can act as a relative proxy for the assemblage distribution and may identify deposit- and even district-scale geochemical halos that can be utilized in exploration. Anomalous thresholds for pathfinder elements are identified via probability plots (Fig. 4.16). Each pathfinder element is plotted against the N-Score that is derived by the following formula: N-Score = [(Assay – Mean value) / Standard deviation]  The N-Score of zero is equal to the mean value for the data set. In addition, potential anomalies are compared with common crustal abundances of pathfinder elements and in fresh rocks (Table 4.4) dominantly derived from the lithologic equivalent Nicola group (see section geologic setting above). In order to highlight whether pathfinder elements are affiliated with increased oxidation due to the influence of hydrothermal alteration, each sample enriched in V > 300ppm is distinguished in the probability plots (Fig. 4.16).  168  Figure 4.16: Probability plots based on the N-Score distribution of pathfinder elements in correlation with the four main mineral assemblages identified in the molar K-Al-Ca ternary and ratio plots above. The common crustal contamination value or background level of each pathfinder element is indicated in the upper left corner of each Nscore plot. These values are more specifically defined in table 2.  169  Table 4.4: Trace element concentrations of fresh rocks of the Nicola group (Quesnell terrane) provided by S. Vaca (MDRU) were used as a direct analogue to the chronologic and tectonic co-eval Stuhini group (Stikine terrane). Where specific element analyses are unavailable, average crustal contamination values werederived from Berkman (2001) and marked with (*). Element  As  Bi  Cu  Li  Rb  S  Sc  Sb  Se  Sr  Te  TiO2  Tl  V  I.D.  ppm  ppm  ppm  ppm  ppm  ppm  ppm  ppm  ppm  ppm  ppm  %  ppm  ppm  PSV001  n/a  n/a  63.00  n/a  44.00  n/a  n/a  n/a  n/a  573.00  n/a  0.59  <0.5  246.00  PSV002  n/a  n/a  63.00  n/a  32.90  n/a  n/a  n/a  n/a  1100.00  n/a  0.50  <0.5  216.00  PSV003  n/a  n/a  159.00  n/a  49.20  n/a  n/a  n/a  n/a  641.00  n/a  0.65  <0.5  266.00  PSV007  n/a  n/a  135.00  n/a  45.70  n/a  n/a  n/a  n/a  931.00  n/a  0.89  <0.5  256.00  PSV009  n/a  n/a  126.00  n/a  65.50  n/a  n/a  n/a  n/a  934.00  n/a  0.74  <0.5  265.00  PSV016  n/a  n/a  63.00  n/a  53.80  n/a  n/a  n/a  n/a  507.00  n/a  0.52  <0.5  249.00  PSV017  n/a  n/a  71.00  n/a  43.80  n/a  n/a  n/a  n/a  644.00  n/a  0.52  <0.5  218.00  PSV028  n/a  n/a  54.00  n/a  15.20  n/a  n/a  n/a  n/a  493.00  n/a  0.89  <0.5  279.00  PSV039  n/a  n/a  279.00  n/a  17.40  n/a  n/a  n/a  n/a  708.00  n/a  0.53  <0.5  188.00  PSV048  n/a  n/a  157.00  n/a  62.10  n/a  n/a  n/a  n/a  902.00  n/a  0.50  <0.5  212.00  1.8-2*  0.15-0.17*  117.00  10-20*  42.96  ?*  10-16*  0.2*  0.05*  743.30  0.001*  0.63  <0.5  239.50  0.16  0.00  29.33  Mean STDV  70.59  16.88  208.99  170  The geology and spatial distribution of mineral and sulfide assemblages in the NGL has been established in chapters 2 and 3. The provided maps are the basis for the correlation of anomalous pathfinder element values with potential host minerals. In addition, their distribution patterns provide indicators toward the lithological controls and the overall physicochemical conditions during their deposition. Overall, four groups of spatially and in part chemically overlapping pathfinder elements are recognized.  In general, the four groups are inclined  westward, sub-parallel to the distribution of rock contacts and alteration assemblages. Group 1 – V, Cu, S, and Se Vanadium values are very high throughout the entire dataset, but is particularly elevated in the calc-potassic and potassic (1) and (2) mineral assemblages due to the association of V(3+, 4+, or 5+)  with Fe3+-bearing minerals and oxides such as andradite, biotite, magnetite, and hematite  (Fig. 4.16). Spatially, elevated V trends from the western base of the combined cross-section to the center and then into the shallower portion of the combined section dominated by felsic rock units and hydrothermal breccias (Fig. 4.17).  171  172  Figure 4.17: Distribution of pathfinder elements associated with group 1 (V, Cu, S, and Se) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, whereas the footprint of highest values is shown in red. See inserted key for the remaining colour code.  Unlike Vanadium, most pathfinder elements are chalcophile and associated with sulfides. Copper is strongly enriched in calc-potassic and potassic (1) mineral assemblages and hosted by chalcopyrite and bornite. It is depleted in pyrite-dominated potassic (2) and more acidic mineral assemblages (Fig. 4.16). The Cu footprint is narrow and trends from the western base of the combined cross-section to the center (Fig. 4.17). It is also spatially coincident with the litholgical contacts of felsic and mafic rock units, as well as the hydrothermal breccias body both in the NGL and CRZ. Sulfur and Se are not only prominent in the calc-potassic and potassic (1) mineral assemblages, but also in the potassic (2) and, in the case Se, in the sericitic assemblages (Fig. 4.16). This reflects the association with Fe-bearing sulfides in addition to Cu, Au, and Agbearing sulfides. Sulfur and Se widely overlap with the Cu footprint, but extend towards the shallow central portion of the combined cross-section where main stage and propylitic pyrite prevails. Group 2 – Te, Bi, and As Tellurium reports moderately high values in the calc-potassic and potassic (1) assemblages (Fig. 4.16). It is also elevated in potassic (2) and sericitic assemblages. Tellurium is broadly coincident with the Cu zone (Fig. 4.18), but expands towards the shallow center-east of the combined section, where Bi is dominant (Fig. 4.18). Bi is highly enriched in the calc-potassic and more acidic levels of the system (Fig. 4.16). Arsenic content is low overall, but increases in the calc-potassic and potassic (2) assemblage (Fig. 4.16). It roughly coincides with the distribution of Bi and is most prominent in the center-east of the profile (Fig. 4.18). All three elements are likely to be incorporated in pyrite, and therefore dominate in the main stage pyrite halo and outer propylitic zone.  173  174  Figure 4.18: Distribution of pathfinder elements associated with group 2 (Te, Bi, and As) and group 3 (Li) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, whereas the footprint of highest values for group 2 is shown in green and for group 3 is shown in blue. See inserted key for the remaining colour code.  Group 3 – Li and Tl Lithium has high overall values, particularly in the potassic (2) and sericitic mineral assemblages (Fig. 4.16). The Li footprint extends from the center to easternmost portion of the combined cross-section (Fig. 4.18), where it correlates closerly with mafic rock units and SAC/propyllitic alteration zone. This association is based on the presence of chlorite, in which Li+ tends to substitutes for Mg2+. Thallium is only slightly enriched and, like Li, is associated with the potassic (2) and sericitic alteration assemblage (Fig. 4.16). It roughly coincides with Li in the east of the combined cross-section, but is absent in the center (Fig. 4.19). Thallium substitutes for K+ in white mica, but also in pyrite. It is strongly biased towards more acid assemblages and is depleted in Ca and K-rich rocks. Thus, the core of the system shows Tl depletion or normal crustal background levels, whereas the outer region show lightly elevated values.  175  Figure 4.19: Distribution of pathfinder elements associated with group 3 (Tl) and 4 (Sb) on the combined NGL and CRZ sections. The footprint of moderately high values is illustrated in grey, whereas the footprint of highest values for group 3 is shown in blue and for group 4 is shown in yellow. See inserted key for the remaining colour code.  176  Group 4 – Sb Antimony reports at significant levels, and is strongly associated with potassic (1) and the sericitic mineral assemblages. It is commonly found in association with pyrite both of the main and propylitic alteration stage. Thus, Sb is most abundant in the easternmost portions of the NGL and CRZ, as well as the shallow western and central section where post-mineral monzonitic intrusions are the dominant host rock.  4.7 Discussion In order to define the physicochemical conditions that drove sulfide mineralization in the NGL and CRZ, the results of the S-isotopic and litho-geochemical analyses need to be individually assessed and correlated. Ohmoto and Rye (1979) noted that the typical range of δ34Ssulfide and δ34Ssulfate in porphyry deposits is -3 to +1‰ and +8 to +15‰ respectively (Fig. 4.5). The NGL and CRZ deposits, however, display a much wider breath of δ34S values (Figs. 4.7 and 4.9). In most alkalic porphyry deposits, the most negative δ34Ssulfide values are directly associated with high grade CuAu ore, and are surrounded by a halo of increasingly positive δ34S signatures (Wilson et al., 2007). In the NGL and CRZ, however, moderately negative δ34Ssulfide values show a high grade affiliation instead (Fig. 4.8). Mineralization and the contoured S-isotopic values in both the NGL and CRZ are oriented sub-parallel to the host rocks and intrusions, dipping at 45-60°W. This strongly supports inferences of a tilted hydrothermal system (Micko et al., in review; chapter 3), and suggests the mineralized fluids rose from a magmatic source such as a batholith or pluton located somewhere down the flow path at depth. Fluids were channelled upward along the syenitic intrusions and along the inclined lithological contacts. 177  Based on the assumption that hydrothermal fluids are of magmatic origin, the following fractionation mechanisms could have led to the observed δ34S zonation pattern. Ohmoto and Rye (1979) showed that spatial variations of δ34S reflect changes in temperature and oxidation state (H2S/SO4) of fluids after their exsolution from the magma at constant composition of bulk sulfur (δ34SΣS). Cooling of a magmatic fluid with a starting composition of ~ 0‰ and a temperature between 600°C and 300ºC will result in steadily decreasing δ34Ssulfide compositions. The magnitude of this shift is greater under oxidising conditions than under reducing conditions, but does not commonly exceed the range of -3 to +1‰ (Ohmoto, 1972; Ohmoto and Rye, 1979; Rye, 1993; Wilson et al., 2007). The trends to even lighter δ34Ssulfide compositions observed in the NGL and CRZ suggest that temperature-controlled S-isotope fractionation alone cannot account for the observed range of δ34Ssulfide values. In addition to temperature, either the oxidation state of the fluid and/or bulk sulfur δ34SΣS may have changed (Wilson et al., 2007), which will be discussed below. On the basis of in equilibrium sulfate-sulfide mineral pairs derived from the early main stage potassic and later stage calc-potassic events, a general temperature range for the hydrothermal system development of 454°C to 591°C was established. On the basis of these temperature variations, the hydrothermal system was sulfate-rich (XSO42-(aq) ~0.80) with an estimated δ34SΣS at ~-3‰. However, the overall regression trend suggests that variations in the H2S/ SO42- ratio and possibly δ34SΣS due to contamination from an isotopically distinct external source and temperature changes are collectively responsible for δ34S isotopic zonation in the NGL and CRZ. The incorporation of an external, isotopically light sulfur source such as biogenic sulfide, which is characteristically depleted in 34S, can lead to the extreme fractionation of S-isotopes as observed in the NGL and CRZ (Ohmoto and Rye, 1979). Shannon et al. (1983) proposed such a mechanism for the Central Zone. However, a biogenic 34S source is not known from within the 178  volcanic rocks of the Galore Creek district. An alternative mechanism is the introduction of sulfur from an inorganic source such as seawater. Sulfate reduction was first suggested from isotopic and fluid inclusion studies of volcanic-hosted massive sulphide deposits (Ohmoto et al., 1970; Ohmoto and Rye, 1979), in which the sulfate source was interpreted to have been seawater. At temperatures of >250°C, seawater sulfate is reduced through reaction with Fe2+ to yield hydrothermal sulfides with δ34S compositions slightly elevated above those of sulfides precipitated from a magmatic fluid (Alt, 1995; Huston et al., 2001; Wilson et al., 2007). The Galore Creek district and the dominant portion of alkalic porphyry deposits in B.C. are hosted in submarine rocks, but whether the deposit formed in a subaerial or subaqueous setting is unknown. Hence, it is possible either that seawater derived sulfur might have been introduced via convection or from trapped connate fluids. However, there is no evidence to further evaluate the possibility. A more plausible sulfur source to have influenced isotopic fractionation in the NGL and CRZ is the volcanic wall-rocks. In such a scenario, the  34  S-enriched aqueous sulfate  species carried in the hydrothermal fluid is reduced through the interaction with primary Fe2+bearing minerals such as pyroxene, biotite, and magnetite (Ohmoto and Lasaga, 1982; Wilson et al., 2007). The oxidation of Fe2+ to Fe3+ in the host rock reduces the hydrothermal fluid by increasing the aqueous H2S/SO4 ratio, and gradually liberates S to be utilized in sulfide generation (Ohmoto and Lasaga, 1982; Wilson et al., 2007; Jago, 2008). The same Fe-bearing minerals that deliver iron to the fluid system are also the focal points for sulfide-mineralization (i.e. commonly observed replacement of biotite and magnetite with chalcopyrite). In order to develop an understanding of the interplay of fluid and metal components during the first and second mineralization event, the data is compared to a log fO2 – log fH2vs. pH diagram at 300°C (Fig. 4.20). It is important, however, to note that the mineral stability and aqueous species predominance fields as well as the gold solubility contours are calculated for a temperature of 300°C, whereas sulfate-sulfide pairs and mineral assemblages suggest higher 179  temperatures of formation. The phase-diagram presented was produced for epithermal high sulfidation deposit research. Unfortunately no diagram that takes a porphyry temperature range of 400 to 600°C into account is currently available. Nonetheless, the log fO2 – log fH2vs. pH diagram does illustrate the intrinsic controls on metals in the Central Zone systems.  Figure 4.20: Log fO2 – log H2 versus pH diagram at 300°C showing the stability fields of Fe-oxides and sulfides (blue), K-felspar and muscovite (pink), aqueous sulfur-bearing species (dotted black line), gold solubility contours (grey to orange), and the predominance fields of Au(HS)2-, AuHS, and AuCl2- (green). The pink ellipse represents the estimated fluid composition during early main stage potassic mineralization event, whereas the brown one represents the later main stage calc-potassic mineralization event. Modified after Tunks (1996) and Cooke and Simmons (2000).  First main stage mineralization The first main stage mineralization event was associated with highly oxidizing, Kbearing fluids that led to extensive K-feldspar, biotite, and anhydrite alteration. In the NGL, the strongly confined and westerly inclined position of the high grade bornite + chalcopyrite shell 180  implies that early mineralized fluids were expelled from the porphyry intrusions and subjacent batholith, and deposited on the contact with the volcano-sedimentary rock units. The interaction of sulfate-rich (SO42-(aq)) fluids with Fe2+ bearing minerals in the mafic volcanic rocks led to the increase of the H2S/SO42- ratio and liberation of S. Along the immediate contact and strongest redox gradient, bornite + chalcopyrite formed that acted as a sink for S, Au, and a large portion of Cu. Due to the redox shift, the δ34Ssulfide values are moderately negative. The chalcopyrite and pyrite halo deposited at greater distance to the redox boundary is characterized by highly negative δ34Ssulfide values and a negligible Au content. A side effect of this redox reaction is hematite and hematite-dusted orthoclase alteration that forms marginal to the high grade ore shell (Micko et al., in review; chapter 3). This provides yet another piece of evidence for the occurrence of inorganic sulfate reduction (Bowman et al., 1987; Wilson et al., 2007; Jago, 2008). Hematite may be produced by the following reaction:  8FeO(rock) + SO42-(aq) + 2H+(aq) ⇔ 4Fe2O3(s) + H2S(aq)  In the CRZ, much of the mineralogical evidence for the first stage mineralization event has been removed during the emplacement of the hydrothermal breccia body. The association of early bornite + chalcopyrite with an early potassic assemblage of K-feldspar, biotite, anhydrite, and hematite implies that a similar mechanism for sulfide precipitation may have acted. When compared to a log fO2 – log fH2 vs. pH diagram at 300°C (Fig. 4.20) the precipitation of distal hematite as well as the abrupt increase in the H2S/SO42- ratio and Au grade proximal to the redox boundary imply a log fO2 value of ~ -31 to -29 and a pH value of ~5.2 (Kfeldspar stability) to 7 (hematite-magnetite boundary and reduced Au solubility). Gold solubility here is greatly dependent on the H2S/SO42- ratio and/or small changes in fO2 and pH. Pyrite is known to lack Au, which implies the Au solubility was low. In addition, Au solubility contours 181  fall into the field of Au(HS)2- and Au was likely to be carried as a (bi-)sulfide complex (Fig. 4.20). Second main stage mineralization The second mineralization event is associated with the introduction of calc-potassic fluids that followed the formation of a hydrothermal breccia body in the CRZ to the NGL. This hydrothermal mineralization event is separated into two stages. One is the formation of calcpotassic silicates, whereas the second is sulfide and sulfate precipitation. In the NGL, calc-potassic stage 1 was moderately oxidizing and formed diopside, andradite, biotite, and magnetite. Stage 2 led to the chalcopyrite + pyrite with minor amounts of bornite and abundant anhydrite along the contact between the breccia body and the westerly inclined contact between felsic and mafic rock units. The chemical mechanism that applied here is similar to the one described for the potassic ore assemblage. Abundant anhydrite combined with high V contents observed in all calc-potassic samples implies excess of Ca and SO42 and a very high oxidation state for the fluid. The interaction of this fluid with Fe2+ bearing cementminerals in the breccias body and the mafic volcanic rock units led to the precipitation of sulfides. The δ34Ssulfide values here are moderately negative, which is again indicative of redoxinduced precipitation of sulfides. The same mechanism operated on a larger scale in the CRZ. The core of the breccia body is dominated by an oxidized mineral assemblage of andradite and minor biotite, whereas the apex is cemented by a more reduced assemblage of andradite, biotite, and magnetite with minor diopside. This change in mineralogy forms a distinct redox gradient that influences sulfide precipitation in the system. The core of the breccia is dominated by anhydrite and small amounts of pyrite + chalcopyrite. The δ34Ssulfide values here are the most negative ones encountered. Towards